Organometallic complex and light emitting element, light emitting device, and electronic device using the organometallic complex

ABSTRACT

An organometallic complex having a structure represented by the following general formula (G1) is provided. 
                         
(In the formula, A represents an aromatic hydrocarbon group having 6 to 25 carbon atoms. Further, Z represents any one of hydrogen, an alkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, or an aryl group having 6 to 25 carbon atoms. In addition, A r   1  represents an aryl group having 6 to 25 carbon atoms. R 1  represents any one of hydrogen, an alkyl group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbon atoms. Further, M is a central metal and represents an element belonging to Group 9 or Group 10.)

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an organometallic complex. Inparticular, the present invention relates to an organometallic complexthat is capable of converting a triplet excited state into luminescence.In addition, the present invention relates to a light emitting element,a light emitting device and an electronic device which use theorganometallic complex.

2. Description of the Related Art

Organic compounds are brought into an excited state by absorbing light.Through this excited state, various reactions (such as photochemicalreactions) are caused in some cases, or luminescence is generated insome cases. Therefore, various applications of the organic compoundshave been made.

As one example of the photochemical reactions, a reaction (oxygenaddition) of singlet oxygen with an unsaturated organic molecule isknown (refer to Reference 1: Haruo INOUE, et al., Basic Chemistry CoursePHOTOCHEMISTRY I (Maruzen Co., Ltd.), pp. 106-110, for example). Sincethe ground state of an oxygen molecule is a triplet state, oxygen in asinglet state (singlet oxygen) is not generated by a directphotoexcitation. However, in the presence of another triplet excitedmolecule, singlet oxygen is generated, which can lead to an oxygenaddition reaction. In this case, a compound that can become the tripletexcited molecule is referred to as a photo sensitizer.

As described above, in order to generate singlet oxygen, aphotosensitizer that can become a triplet excited molecule byphotoexcitation is necessary. However, since the ground state of anordinary organic compound is a singlet state, photoexcitation to atriplet excited state is a forbidden transition, and a triplet excitedmolecule is not easily generated. Therefore, as such a photosensitizer,a compound in which intersystem crossing from the singlet excited stateto the triplet excited state easily occurs (or a compound which allowsthe forbidden transition of photoexcitation directly to the tripletexcited state) is required. In other words, such a compound can be usedas a photosensitizer and is useful.

Also, such a compound often emits phosphorescence. The phosphorescenceis luminescence generated by transition between different energies inmultiplicity and, in the case of an ordinary organic compound, thephosphorescence indicates luminescence generated in returning from thetriplet excited state to the singlet ground state (in contrast,luminescence in returning from a singlet excited state to the singletground state is referred to as fluorescence). Application fields of acompound capable of emitting phosphorescence, that is, a compoundcapable of converting a triplet excited state into luminescence(hereinafter, referred to as a phosphorescent compound), include a lightemitting element using an organic compound as a light emittingsubstance.

This light emitting element has a simple structure in which a lightemitting layer including an organic compound that is a light emittingsubstance is provided between electrodes. This light emitting element isa device attracting attention as a next-generation flat panel displayelement in terms of characteristics such as being thin and light inweight, high speed response, and direct current low voltage driving. Inaddition, a display device using this light emitting element is superiorin contrast, image quality, and wide viewing angle.

The emission mechanism of a light emitting element in which an organiccompound is used as a light emitting substance is a carrier injectiontype. Namely, by applying voltage with a light emitting layer interposedbetween electrodes, electrons and holes injected from the electrodes arerecombined to make the light emitting substance excited, and light isemitted in returning from the excited state to the ground state. As thetype of the excited state, as in the case of photoexcitation describedabove, a singlet excited state (S*) and a triplet excited state (T*) arepossible. Further, the statistical generation ratio thereof in a lightemitting element is considered to be S*:T*=1:3.

As for a compound capable of converting a singlet excited state toluminescence (hereinafter, referred to as a fluorescent compound),luminescence from a triplet excited state (phosphorescence) is notobserved but only luminescence from a singlet excited state(fluorescence) is observed at a room temperature. Accordingly, theinternal quantum efficiency (the ratio of generated photons to injectedcarriers) in a light emitting element using a fluorescent compound isassumed to have a theoretical limit of 25% based on S*:T*=1:3.

On the other hand, when the phosphorescent compound described above isused, the internal quantum efficiency can be improved to 75 to 100% intheory. Namely, a light emission efficiency that is 3 to 4 times as muchas that of the fluorescence compound can be achieved. For these reasons,in order to achieve a highly-efficient light emitting element, a lightemitting element using a phosphorescent compound has been developedactively (for example, refer to Reference 2: Zhang, Guo-Lin, et al.,Gaodeng Xuexiao Huaxue Xuebao (2004), vol. 25, No. 3, pp. 397-400). Inparticular, as the phosphorescent compound, an organometallic complexusing iridium or the like as a central metal has been attractingattention, owing to its high phosphorescence quantum yield.

SUMMARY OF THE INVENTION

The organometallic complex disclosed in Reference 2 can be expected tobe used as a photosensitizer, since it easily causes intersystemcrossing. In addition, since the organometallic complex easily generatesluminescence (phosphorescence) from a triplet excited state, a highlyefficient light emitting element is expected by using the organometalliccomplex for the light emitting element. However, in the present state,the number of types of such organometallic complexes is small.

The organometallic complex disclosed in Reference 2 emits orange-colorlight. When the organometallic complex is used for a full-color display,color purity as a red color is poor, which is a disadvantage in terms ofcolor reproductivity. In contrast, in the case where the light emissioncolor is in a dark red region; in other words, where the emissionwavelength is extremely long, the organometallic complex is advantageousin terms of color reproductivity; however, the luminous efficiency(cd/A) decreases.

In consideration of the above-described problems, it is an object of thepresent invention to provide an organometallic complex by whichred-color light emission can be obtained. It is another object of thepresent invention to provide an organometallic complex with high lightemission efficiency. Further, it is still another object of the presentinvention to provide an organometallic complex by which red-color lightemission with high luminous efficiency (cd/A) can be obtained.

Furthermore, the present invention aims to provide a light emittingelement with high light emission efficiency. In addition, the presentinvention aims to provide a light emitting element by which red-colorlight emission with high luminous efficiency can be obtained. Further,the present invention aims to provide a light emitting device and anelectronic device with reduced power consumption.

The present inventors have made researches earnestly. As a result, thepresent inventors have found that a pyrazine derivative represented bythe following general formula (G0) is ortho-metalated with a metal ionof Group 9 or Group 10, thereby obtaining an organometallic complex. Inaddition, the present inventors have also found that the organometalliccomplex easily causes intersystem crossing and can emit phosphorescenceefficiently. Further, they have also found that the light emission colorof the organometallic complex is favorable red color.

(In the formula, A represents an aromatic hydrocarbon group having 6 to25 carbon atoms. Further, Z represents any one of hydrogen, an alkylgroup having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbonatoms, or an aryl group having 6 to 25 carbon atoms. In addition, A_(r)¹ represents an aryl group having 6 to 25 carbon atoms. R¹ representsany one of hydrogen, an alkyl group having 1 to 4 carbon atoms, or analkoxy group having 1 to 4 carbon atoms.)

Accordingly, the structure of the present invention is an organometalliccomplex having a structure represented by the following general formula(G1).

(In the formula, A represents an aromatic hydrocarbon group having 6 to25 carbon atoms. Further, Z represents any one of hydrogen, an alkylgroup having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbonatoms, or an aryl group having 6 to 25 carbon atoms. In addition, A_(r)¹ represents an aryl group having 6 to 25 carbon atoms. R¹ representsany one of hydrogen, an alkyl group having 1 to 4 carbon atoms, or analkoxy group having 1 to 4 carbon atoms. Further, M is a central metaland represents an element belonging to Group 9 or Group 10.)

In the case where Z in the above general formula (G0) is an aryl group,the organometallic complex of the present invention has a structurerepresented by the following general formula (G2). Accordingly, anotherstructure of the present invention is an organometallic complex havingthe structure represented by the following general formula (G2).

(In the formula, A represents an aromatic hydrocarbon group having 6 to25 carbon atoms. Further, each of A_(r) ¹ and A_(r) ² represents an arylgroup having 6 to 25 carbon atoms. R¹ represents any one of hydrogen, analkyl group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4carbon atoms. Further, M is a central metal and represents an elementbelonging to Group 9 or Group 10.)

When the organometallic complex of the present invention is evaporatedfor the purpose of sublimation, purification, or the like, it ispreferable to use a substituted or unsubstituted 1,2-phenylene group asthe aromatic hydrocarbon group A in the above general formula (G2),since the use of the substituted or unsubstituted 1,2-phenylene groupcan suppress the increase of the evaporation temperature due to theincrease of molecular weight. In this case, a substituted orunsubstituted phenyl group is preferably used as A_(r) ² for ease ofsynthesis. Accordingly, a preferable structure of the present inventionis an organometallic complex having a structure represented by thefollowing general formula (G3).

(In the formula, A_(r) ¹ represents an aryl group having 6 to 25 carbonatoms. R¹ represents any one of hydrogen, an alkyl group having 1 to 4carbon atoms, or an alkoxy group having 1 to 4 carbon atoms. Further,each of R³ to R¹¹ represents any one of hydrogen, an alkyl group having1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, an arylgroup having 6 to 12 carbon atoms, a halogen group, or a trifluoromethylgroup. Further, M is a central metal and represents an element belongingto Group 9 or Group 10.)

Further, a favorable structure of the above general formula (G2) can beobtained when the aromatic hydrocarbon group A is an unsubstitutedphenylen group. In this case, an unsubstituted phenyl group ispreferably used for A_(r) ² for ease of synthesis. Accordingly, a morepreferable structure of the present invention is an organometalliccomplex having a structure represented by the following general formula(G4).

(In the formula, A_(r) ¹ represents an aryl group having 6 to 25 carbonatoms. R¹ represents any one of hydrogen, an alkyl group having 1 to 4carbon atoms, or an alkoxy group having 1 to 4 carbon atoms. Further, Mis a central metal and represents an element belonging to Group 9 orGroup 10.)

Further, when A_(r) ¹ is a substituted or unsubstituted phenyl group inthe general formula (G4), red-color light emission with excellent colorpurity and high luminous efficiency (cd/A) can be obtained. Accordingly,a further preferable structure of the present invention is anorganometallic complex having a structure represented by the followinggeneral formula (G5).

(In the formula, R¹ represents any one of hydrogen, an alkyl grouphaving 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbonatoms. Further, each of R¹² to R¹⁶ represents any one of hydrogen, analkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4carbon atoms, an aryl group having 6 to 12 carbon atoms, a halogengroup, or a trifluoromethyl group. Further, M is a central metal andrepresents an element belonging to Group 9 or Group 10.)

In the general formula (G5), hydrogen, a fluoro group, or atrifluoromethyl group is preferable as each of R¹² to R¹⁶. By takingsuch a structure, red-color light emission having a chromaticity nearthe red-color chromaticity set by NTSC (National Television StandardsCommittee) (i.e., (x, y)=(0.67, 0.33)) can be obtained.

Next, in the case where Z in the above general formula (G0) is hydrogen,an alkyl group, or an alkoxy group, the organometallic complex of thepresent invention has a structure represented by the following generalformula (G6). Accordingly, another structure of the present invention isan organometallic complex having the structure represented by thefollowing general formula (G6).

(In the formula, A represents an aromatic hydrocarbon group having 6 to25 carbon atoms. A_(r) ¹ represents an aryl group having 6 to 25 carbonatoms. Each of R¹ and R² represents any one of hydrogen, an alkyl grouphaving 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbonatoms. Further, M is a central metal and represents an element belongingto Group 9 or Group 10.)

When the organometallic complex of the present invention is evaporatedfor the purpose of sublimation, purification, or the like, it ispreferable to use a substituted or unsubstituted 1,2-phenylene group asthe aromatic hydrocarbon group A in the above general formula (G6),since the use of the substituted or unsubstituted 1,2-phenylene groupcan suppress the increase of the evaporation temperature due to theincrease of molecular weight. Accordingly, a preferable structure of thepresent invention is an organometallic complex having a structurerepresented by the following general formula (G7).

(In the formula, A_(r) ¹ represents an aryl group having 6 to 25 carbonatoms. Each of R¹ and R² represents any one of hydrogen, an alkyl grouphaving 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbonatoms. Further, each of R³ to R⁶ represents any one of hydrogen, analkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4carbon atoms, an aryl group having 6 to 12 carbon atoms, a halogengroup, or a trifluoromethyl group. Further, M is a central metal andrepresents an element belonging to Group 9 or Group 10.)

Further, a favorable structure of the above general formula (G6) can beobtained when the aromatic hydrocarbon group A is an unsubstitutedphenylen group. Accordingly, a more preferable structure of the presentinvention is an organometallic complex having a structure represented bythe following general formula (G8).

(In the formula, A_(r) ¹ represents an aryl group having 6 to 25 carbonatoms. Each of R¹ and R² represents any one of hydrogen, an alkyl grouphaving 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbonatoms. Further, M is a central metal and represents an element belongingto Group 9 or Group 10.)

Further, when A_(r) ¹ is a substituted or unsubstituted phenyl group inthe general formula (G8), red-color light emission with excellent colorpurity and high luminous efficiency (cd/A) can be obtained. Accordingly,a further preferable structure of the present invention is anorganometallic complex having a structure represented by the followinggeneral formula (G9).

(In the formula, each of R¹ and R² represents any one of hydrogen, analkyl group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4carbon atoms. Further, each of R¹² to R¹⁶ represents any one ofhydrogen, an alkyl group having 1 to 4 carbon atoms, an alkoxy grouphaving 1 to 4 carbon atoms, an aryl group having 6 to 12 carbon atoms, ahalogen group, or a trifluoromethyl group. Further, M is a central metaland represents an element belonging to Group 9 or Group 10.)

In the general formula (G9), hydrogen, a fluoro group, or atrifluoromethyl group is preferable as each of R¹² to R¹⁶. By takingsuch a structure, red-color light emission having a chromaticity nearthe red-color chromaticity set by NTSC (National Television StandardsCommittee) (i.e., (x, y)=(0.67, 0.33)) can be obtained.

When hydrogen or a methyl group is used as R¹ in the pyrazine derivativerepresented by the above general formula (G0), steric hindrance of thepyrazine derivative is reduced and the pyrazine derivative is easilyortho-metalated with a metal ion, which is preferable in terms of asynthesis yield. Accordingly, a preferable structure of the presentinvention is an organometallic complex having a structure represented byany of the general formulae (G1) to (G9), in which R¹ is hydrogen or amethyl group.

Here, as the organometallic complex having the structure represented bythe above general formula (G1), an organometallic complex represented bythe following general formula (G10) is more specifically preferablebecause it can be easily synthesized.

(In the formula, A represents an aromatic hydrocarbon group having 6 to25 carbon atoms. Further, Z represents any one of hydrogen, an alkylgroup having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbonatoms, or an aryl group having 6 to 25 carbon atoms. In addition, A_(r)¹ represents an aryl group having 6 to 25 carbon atoms. R¹ representsany one of hydrogen, an alkyl group having 1 to 4 carbon atoms, or analkoxy group having 1 to 4 carbon atoms. Further, M is a central metaland represents an element belonging to Group 9 or Group 10. L representsa monoanionic ligand. In addition, n is 2 when the central metal is anelement belonging to Group 9, and n is 1 when the central metal is anelement belonging to Group 10.)

As the organometallic complex having the structure represented by theabove general formula (G2), an organometallic complex represented by thefollowing general formula (G11) is preferable because it can be easilysynthesized.

(In the formula, A represents an aromatic hydrocarbon group having 6 to25 carbon atoms. Further, each of A_(r) ¹ and A_(r) ² represents an arylgroup having 6 to 25 carbon atoms. R¹ represents any one of hydrogen, analkyl group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4carbon atoms. Further, M is a central metal and represents an elementbelonging to Group 9 or Group 10. L represents a monoanionic ligand. Inaddition, n is 2 when the central metal is an element belonging to Group9, and n is 1 when the central metal is an element belonging to Group10.)

As the organometallic complex having the structure represented by theabove general formula (G3), an organometallic complex represented by thefollowing general formula (G12) is preferable because it can be easilysynthesized.

(In the formula, A_(r) ¹ represents an aryl group having 6 to 25 carbonatoms. R¹ represents any one of hydrogen, an alkyl group having 1 to 4carbon atoms, or an alkoxy group having 1 to 4 carbon atoms. Further,each of R³ to R¹ represents any one of hydrogen, an alkyl group having 1to 4 carbon atoms, an alkoxy group having 1 to 4 carbon atoms, an arylgroup having 6 to 12 carbon atoms, a halogen group, or a trifluoromethylgroup. Further, M is a central metal and represents an element belongingto Group 9 or Group 10. L represents a monoanionic ligand. In addition,n is 2 when the central metal is an element belonging to Group 9, and nis 1 when the central metal is an element belonging to Group 10.)

As the organometallic complex having the structure represented by theabove general formula (G4), an organometallic complex represented by thefollowing general formula (G13) is specifically preferable because itcan be easily synthesized.

(In the formula, A_(r) ¹ represents an aryl group having 6 to 25 carbonatoms. R¹ represents any one of hydrogen, an alkyl group having 1 to 4carbon atoms, or an alkoxy group having 1 to 4 carbon atoms. Further, Mis a central metal and represents an element belonging to Group 9 orGroup 10. L represents a monoanionic ligand. In addition, n is 2 whenthe central metal is an element belonging to Group 9, and n is 1 whenthe central metal is an element belonging to Group 10.)

As the organometallic complex having the structure represented by theabove general formula (G5), an organometallic complex represented by thefollowing general formula (G14) is specifically preferable because itcan be easily synthesized.

(In the formula, R¹ represents any one of hydrogen, an alkyl grouphaving 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbonatoms. Further, each of R¹² to R¹⁶ represents any one of hydrogen, analkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4carbon atoms, an aryl group having 6 to 12 carbon atoms, a halogengroup, or a trifluoromethyl group. Further, M is a central metal andrepresents an element belonging to Group 9 or Group 10. L represents amonoanionic ligand. In addition, n is 2 when the central metal is anelement belonging to Group 9, and n is 1 when the central metal is anelement belonging to Group 10.)

In the general formula (G14), hydrogen, a fluoro group, or atrifluoromethyl group is preferable as each of R¹² to R¹⁶. By takingsuch a structure, red-color light emission having a chromaticity nearthe red-color chromaticity set by NTSC (National Television StandardsCommittee) (i.e., (x, y)=(0.67, 0.33)) can be obtained.

As the organometallic complex having the structure represented by theabove general formula (G6), an organometallic complex represented by thefollowing general formula (G15) is specifically preferable because itcan be easily synthesized.

(In the formula, A represents an aromatic hydrocarbon group having 6 to25 carbon atoms. A_(r) ¹ represents an aryl group having 6 to 25 carbonatoms. Each of R¹ and R² represents any one of hydrogen, an alkyl grouphaving 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbonatoms. Further, M is a central metal and represents an element belongingto Group 9 or Group 10. L represents a monoanionic ligand. In addition,n is 2 when the central metal is an element belonging to Group 9, and nis 1 when the central metal is an element belonging to Group 10.)

As the organometallic complex having the structure represented by theabove general formula (G7), an organometallic complex represented by thefollowing general formula (G16) is specifically preferable because itcan be easily synthesized.

(In the formula, A_(r) ¹ represents an aryl group having 6 to 25 carbonatoms. Each of R¹ and R² represents any one of hydrogen, an alkyl grouphaving 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbonatoms. Further, each of R³ to R⁶ represents any one of hydrogen, analkyl group having 1 to 4 carbon atoms, an alkoxy group having 1 to 4carbon atoms, an aryl group having 6 to 12 carbon atoms, a halogengroup, or a trifluoromethyl group. Further, M is a central metal andrepresents an element belonging to Group 9 or Group 10. L represents amonoanionic ligand. In addition, n is 2 when the central metal is anelement belonging to Group 9, and n is 1 when the central metal is anelement belonging to Group 10.)

As the organometallic complex having the structure represented by theabove general formula (G8), an organometallic complex represented by thefollowing general formula (G17) is specifically preferable because itcan be easily synthesized.

(In the formula, A_(r) ¹ represents an aryl group having 6 to 25 carbonatoms. Each of R¹ and R² represents any one of hydrogen, an alkyl grouphaving 1 to 4 carbon atoms, or an alkoxy group having 1 to 4 carbonatoms. Further, M is a central metal and represents an element belongingto Group 9 or Group 10. L represents a monoanionic ligand. In addition,n is 2 when the central metal is an element belonging to Group 9, and nis 1 when the central metal is an element belonging to Group 10.)

As the organometallic complex having the structure represented by theabove general formula (G9), an organometallic complex represented by thefollowing general formula (G18) is specifically preferable because itcan be easily synthesized.

(In the formula, each of R¹ and R² represents any one of hydrogen, analkyl group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4carbon atoms. Further, each of R¹² to R¹⁶ represents any one ofhydrogen, an alkyl group having 1 to 4 carbon atoms, an alkoxy grouphaving 1 to 4 carbon atoms, an aryl group having 6 to 12 carbon atoms, ahalogen group, or a trifluoromethyl group. Further, M is a central metaland represents an element belonging to Group 9 or Group 10. L representsa monoanionic ligand. In addition, n is 2 when the central metal is anelement belonging to Group 9, and n is 1 when the central metal is anelement belonging to Group 10.)

In the general formula (G18), hydrogen, a fluoro group, or atrifluoromethyl group is preferable as each of R¹² to R¹⁶. By takingsuch a structure, red-color light emission having a chromaticity nearthe red-color chromaticity set by NTSC (National Television StandardsCommittee) (i.e., (x, y)=(0.67, 0.33)) can be obtained.

When hydrogen or a methyl group is used as R¹ in the pyrazine derivativerepresented by the above general formula (G0), steric hindrance of thepyrazine derivative is reduced and the pyrazine derivative is easilyortho-metalated with a metal ion, which is preferable in terms of asynthesis yield. Accordingly, a preferable structure of the presentinvention is an organometallic complex represented by any of the abovegeneral formulae (G10) to (G18), in which R¹ is hydrogen or a methylgroup.

The above-mentioned monoanionic ligand L is preferably either amonoanionic bidentate chelate ligand having a β-diketone structure, amonoanionic bidentate chelate ligand having a carboxyl group, amonoanionic bidentate chelate ligand having a phenolic hydroxyl group,or a monoanionic bidentate chelate ligand in which two ligand elementsare both nitrogen, because these ligands have high coordinating ability.More preferably, the monoanionic ligand L is a monoanionic ligandrepresented by the following structural formulae (L1) to (L8). Sincethese ligands have high coordinating ability and can be obtained at lowprice, they are useful.

In order to emit phosphorescence more efficiently, a heavy metal ispreferable as a central metal in terms of heavy atom effect. Therefore,one feature of the present invention is that iridium or platinum isemployed as the central metal M in each of the above organometalliccomplexes of the present invention. Particularly when the central metalM is iridium, heat resistance of the organometallic complex is improved.Therefore, iridium is particularly preferable as the central metal M.

In the organometallic complex having the structure represented by any ofthe above general formulae (G1) to (G9) (in other words, including theorganometallic complexes represented by the above general formulae (G10)to (G18)), the coordinate structure in which the pyrazine derivativerepresented by the general formula (G0) is ortho-metalated with a metalion, contributes emission of phosphorescence greatly. Therefore, anotherstructure of the present invention is a light emitting materialincluding an organometallic complex as described above.

In addition, the organometallic complex of the present invention is veryeffective. Because the organometallic complex of the present inventioncan emit phosphorescence; in other words, a triplet excitation energycan be converted into light, high efficiency can be obtained by applyingthe organometallic complex to a light emitting element. Therefore, thepresent invention includes a light emitting element using theorganometallic complex of the present invention.

At this time, the organometallic complex of the present invention iseffective when it is used for a light emitting substance in terms oflight emission efficiency. Therefore, one feature of the presentinvention is a light emitting element using the organometallic complexof the present invention as a light emitting substance. A light emittingelement having a structure in which a light emitting layer is providedbetween a pair of electrodes and an organometallic complex of thepresent invention is dispersed in a metal complex is preferable.Further, the metal complex is preferably a zinc complex.

The thus obtained light emitting element of the present invention canrealize high light emission efficiency, and thus, a light emittingdevice (such as an image display device or a light emitting device)using this light emitting element can realize low power consumption.Accordingly, the present invention includes a light emitting device andan electronic device using the light emitting element of the presentinvention.

One feature of the light emitting device of the present invention is toinclude a layer containing a light emitting substance between a pair ofelectrodes, in which the layer containing the light emitting substanceincludes a light emitting element containing the above-describedorganometallic complex and a control means which controls light emissionof the light emitting element. In this specification, the term “lightemitting device” refers to an image display device or a light emittingdevice including a light emitting element. Further, the category of thelight emitting device includes a module including a light emittingelement attached with a connector such as a module attached with ananisotropic conductive film, TAB (Tape Automated Bonding) tape, or a TCP(Tape Carrier Package); a module in which an end of the TAB tape or theTCP is provided with a printed wiring board; or a module in which an IC(Integrated Circuit) is directly mounted on a light emitting element byCOG (Chip On Glass); and the like. Further, the category includes alight emitting device used for lighting equipment and the like.

One feature of an electronic device of the present invention is toinclude a display portion, and the display portion includes theabove-described light emitting element and the control means whichcontrols light emission of the light emitting element.

With the use of an organometallic complex of the present invention,red-color light emission can be obtained. Further, the organometalliccomplex of the present invention is an organometallic complex with highlight emission efficiency. In addition, red-color light emission withhigh luminous efficiency (cd/A) can be obtained.

Further, when a light emitting element is manufactured with the use ofthe organometallic complex of the present invention, the light emittingelement can have high light emission efficiency. Further, red-colorlight emission with high luminous efficiency can be obtained.

Further, the usage of the organometallic complex of the presentinvention enables a light emitting device and an electronic device withreduced power consumption to be provided.

BRIEF DESCRIPTION OF DRAWINGS

In the accompanying drawings:

FIG. 1 shows a light emitting element of the present invention;

FIG. 2 shows a light emitting element of the present invention;

FIG. 3 shows a light emitting element of the present invention;

FIGS. 4A and 4B show a light emitting device of the present invention;

FIG. 5 shows a light emitting device of the present invention;

FIGS. 6A to 6D show electronic devices of the present invention;

FIG. 7 shows an electronic device of the present invention;

FIG. 8 shows a lighting device of the present invention;

FIG. 9 shows a lighting device of the present invention;

FIGS. 10A and 10B show a ¹H-NMR chart of(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III);

FIG. 11 shows an absorption spectrum and an emission spectrum of(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III);

FIG. 12 shows a light emitting element of examples;

FIG. 13 shows current density-luminance characteristics of a lightemitting element manufactured in Example 2;

FIG. 14 shows voltage-luminance characteristics of a light emittingelement manufactured in Example 2;

FIG. 15 shows luminance-current efficiency characteristics of a lightemitting element manufactured in Example 2;

FIG. 16 shows luminance-external quantum efficiency characteristics of alight emitting element manufactured in Example 2;

FIG. 17 shows an emission spectrum of a light emitting elementmanufactured in Example 2;

FIG. 18 shows current density-luminance characteristics of a lightemitting element manufactured in Example 3;

FIG. 19 shows voltage-luminance characteristics of a light emittingelement manufactured in Example 3;

FIG. 20 shows luminance-current efficiency characteristics of a lightemitting element manufactured in Example 3;

FIG. 21 shows luminance-external quantum efficiency characteristics of alight emitting element manufactured in Example 3;

FIG. 22 shows an emission spectrum of a light emitting elementmanufactured in Example 3;

FIGS. 23A and 23B show a ¹H-NMR chart of2,3-bis{4-[N-(4-biphenylyl)-N-phenylamino]phenyl} quinoxaline;

FIGS. 24A and 24B show a ¹H-NMR chart of(acetylacetonato)bis(2,3-diphenyl-5-p-tolylpyrazinato)iridium(III);

FIG. 25 shows an absorption spectrum and an emission spectrum of(acetylacetonato)bis(2,3-diphenyl-5-p-tolylpyrazinato)iridium(III);

FIGS. 26A and 26B show a ¹H-NMR chart of(acetylacetonato)bis(5-phenyl-2,3-di-p-tolylpyrazinato)iridium(III);

FIG. 27 shows an absorption spectrum and an emission spectrum of(acetylacetonato)bis(5-phenyl-2,3-di-p-tolylpyrazinato)iridium(III);

FIGS. 28A and 28B show a ¹H-NMR chart ofbis(2,3,5-triphenylpyrazinato)(picolinato)iridium(III);

FIG. 29 shows an absorption spectrum and an emission spectrum ofbis(2,3,5-triphenylpyrazinato)(picolinato)iridium(III);

FIGS. 30A and 30B show a ¹H-NMR chart of(acetylacetonato)bis(3-methyl-2,5-diphenylpyrazinato)iridium(III);

FIG. 31 shows an absorption spectrum and an emission spectrum of(acetylacetonato)bis(3-methyl-2,5-diphenylpyrazinato)iridium(III);

FIG. 32 shows current density-luminance characteristics of a lightemitting element manufactured in Example 8;

FIG. 33 shows voltage-luminance characteristics of a light emittingelement manufactured in Example 8;

FIG. 34 shows luminance-current efficiency characteristics of a lightemitting element manufactured in Example 8;

FIG. 35 shows luminance-external quantum efficiency characteristics of alight emitting element manufactured in Example 8;

FIG. 36 shows an emission spectrum of a light emitting elementmanufactured in Example 8;

FIGS. 37A and 37B show a ¹H-NMR chart of4-(9H-carbazole-9-yl)-4′-(5-phenyl-1,3,4-oxadiazole-2-yl)triphenylamine);

FIGS. 38A and 38B show a ¹H-NMR chart of(acetylacetonato)bis[5-(3-fluorophenyl)2,3-di-p-tolylpyrazinato]iridium(III);and

FIG. 39 shows an absorption spectrum and an emission spectrum of(acetylacetonato)bis[5-(3-fluorophenyl)2,3-di-p-tolylpyrazinato]iridium(III).

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiment modes and examples of the present invention willbe described with reference to the drawings. Note that the presentinvention can be carried out in many various modes. It is easilyunderstood by those skilled in the art that various changes may be madein forms and details without departing from the spirit and the scope ofthe present invention. Therefore, the present invention should not belimited to the description of the embodiment modes and examples below.

Embodiment Mode 1

Embodiment Mode 1 will describe an organometallic complex of the presentinvention.

<Synthetic Method of a Pyrazine Derivative Represented by the GeneralFormula (G0)>

An organometallic complex of the present invention is formed by orthometalation of a pyrazine derivative represented by the following generalformula (G0) with a metal ion belonging to Group 9 or Group 10.

(In the formula, A represents an aromatic hydrocarbon group having 6 to25 carbon atoms. Further, Z represents any one of hydrogen, an alkylgroup having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbonatoms, or an aryl group having 6 to 25 carbon atoms. In addition, A_(r)¹ represents an aryl group having 6 to 25 carbon atoms. R¹ representsany one of hydrogen, an alkyl group having 1 to 4 carbon atoms, or analkoxy group having 1 to 4 carbon atoms.)

Hereinafter, synthetic methods of the pyrazine derivative represented bythe general formula (G0) in each of the cases where Z in the generalformula (G0) is an aryl group (the following general formula (G0-1)) andwhere Z is hydrogen, an alkyl group, or an alkoxy group (the followinggeneral formula (G0-2)) will be described.

(In the formula, A represents an aromatic hydrocarbon group having 6 to25 carbon atoms. Further, each of A_(r) ¹ and A_(r) ² represents an arylgroup having 6 to 25 carbon atoms. R¹ represents any one of hydrogen, analkyl group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4carbon atoms.)

(In the formula, A represents an aromatic hydrocarbon group having 6 to25 carbon atoms. Further, A_(r) ¹ represents an aryl group having 6 to25 carbon atoms. Each of R¹ and R² represents any one of hydrogen, analkyl group having 1 to 4 carbon atoms, or an alkoxy group having 1 to 4carbon atoms.)

First, the pyrazine derivative represented by the general formula (G0-1)can be synthesized by the following simple synthetic scheme. Forexample, the pyrazine derivative can be obtained by reacting a pyrazinederivative (A1) with aryllithium compound or arylmagnesium bromidecompound (A2) as shown in the following scheme (a). Alternatively, thepyrazine derivative can be obtained by reacting a pyrazine derivative(A1′) with aryllithium compound or arylmagnesium bromide compound (A2′)as shown in the following scheme (a′).

On the other hand, the pyrazine derivative represented by the generalformula (G0-2) can be synthesized by the following simple syntheticscheme. For example, the pyrazine derivative can be obtained by reactinga pyrazine derivative (A1″) with aryllithium compound or arylmagnesiumbromide compound (A2″) as shown in the following scheme (a″).Alternatively, in the case where A=A_(r) ¹ and R¹=R²=H, the pyrazinederivative can be obtained by treating α-haloketone (the followingstructural formula (A3)) of arene with the use of NH₃ and throughself-condensation of α-aminoketone of arene. Note that X in thestructural formula (A3) represents a halogen element.

Since various kinds of the above-described compounds (A1), (A2), (A1′),(A2′), (A1″), (A2″), and (A3) are available commercially or can besynthesized, many kinds of the pyrazine derivative represented by theabove-described general formula (G0) can be synthesized.

<Synthetic Method of an Organometallic Complex of the Present InventionHaving a Structure Represented by the General Formula (G1)>

Next, an organometallic complex of the present invention which is formedby ortho metalation of the pyrazine derivative represented by thegeneral formula (G0), i.e., the organometallic complex having thestructure represented by the following general formula (G1) will bedescribed.

(In the formula, A represents an aromatic hydrocarbon group having 6 to25 carbon atoms. Further, Z represents any one of hydrogen, an alkylgroup having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbonatoms, or an aryl group having 6 to 25 carbon atoms. A_(r) ¹ representsan aryl group having 6 to 25 carbon atoms. In addition, R¹ representsany one of hydrogen, an alkyl group having 1 to 4 carbon atoms, or analkoxy group having 1 to 4 carbon atoms. M is a central metal andrepresents an element belonging to Group 9 or Group 10.)

First, as shown in the following synthetic scheme (b), the pyrazinederivative represented by the general formula (G0) and a compound of ametal belonging to Group 9 or Group 10 and including halogen (such as ametal halide or metal complex) are heated in an appropriate solvent,thereby obtaining a dinuclear complex (B) which is a kind oforganometallic complex of the present invention having the structurerepresented by the general formula (G1). As a compound of a metalbelonging to Group 9 or Group 10 and including halogen, there arerhodium chloride hydrate, palladium chloride, iridium chloride hydrate,iridium chloride hydrate hydrochloride, potassiumtetrachloroplatinate(II), and the like; however, the present inventionis not limited to these examples. In the scheme (b), M denotes anelement belonging to Group 9 or Group 10, and X denotes a halogenelement. In addition, n is 2 when M is an element belonging to Group 9,and n is 1 when M is an element belonging to Group 10.

Further, as shown in the following synthetic scheme (c′), the dinuclearcomplex (B) and the pyrazine derivative represented by the generalformula (G0) are heated at a high temperature of about 200° C. in a highboiling solvent of glycerol or the like, and thus, one type (C′) oforganometallic complex of the present invention having the structurerepresented by the general formula (G1) can be obtained. As shown in thefollowing synthetic scheme (c″), a dinuclear complex (B) and a compoundwhich can be ortho-metalated, such as phenylpyridine (more generally, acompound which can be cyclo-metalated) are heated at a high temperatureof about 200° C. in a high boiling solvent of glycerol or the like, andthus, one type (C″) of organometallic complex of the present inventionhaving the structure represented by the general formula (G1) can beobtained. In the schemes (c′) and (c″), M denotes an element belongingto Group 9 or Group 10, and X denotes a halogen element. In addition, nis 2 when M is an element belonging to Group 9, and n is 1 when M is anelement belonging to Group 10.

<Synthetic Method of an Organometallic Complex of the Present InventionRepresented by the General Formula (G10)>

An organometallic complex represented by the general formula (G10),which is a preferable example among organometallic complexes having thestructure represented by the above general formula (G1), will bedescribed.

(In the formula, A represents an aromatic hydrocarbon group having 6 to25 carbon atoms. Further, Z represents any one of hydrogen, an alkylgroup having 1 to 4 carbon atoms, an alkoxy group having 1 to 4 carbonatoms, or an aryl group having 6 to 25 carbon atoms. A_(r) ¹ representsan aryl group having 6 to 25 carbon atoms. Further, R¹ represent any oneof hydrogen, an alkyl group having 1 to 4 carbon atoms, or an alkoxygroup having 1 to 4 carbon atoms. M is a central metal, and denotes anelement belonging to Group 9 or Group 10. L represents a monoanionicligand. In addition, n is 2 when M is an element belonging to Group 9,and n is 1 when M is an element belonging to Group 10.)

The organometallic complex of the present invention represented by theabove general formula (G10) can be synthesized by the following scheme(c). In other words, the dinuclear complex (B) obtained by the abovescheme (b) is reacted with HL which is a material of a monoanionicligand L, and a proton of HL is separated and coordinated to the centralmetal M. In this manner, the organometallic complex of the presentinvention represented by the general formula (G10) can be obtained. Inthe scheme (c), M denotes an element belonging to Group 9 or Group 10,and X denotes a halogen element. In addition, n is 2 when M is anelement belonging to Group 9, and n is 1 when M is an element belongingto Group 10.

<Specific Structural Formulae of the Organometallic Complex of thePresent Invention Having the Structure Represented by the GeneralFormula (G1) and the Organometallic Complex of the Present InventionRepresented by the General Formula (G10)>

Next, specific structural formulae of the organometallic complex of thepresent invention having the structure represented by the generalformula (G1) and the organometallic complex of the present inventionrepresented by the general formula (G10) will be described.

The central metal M is selected from elements belonging to Group 9 orGroup 10; however, iridium(III) or platinum(II) is preferable in termsof light emission efficiency. In particular, iridium(III) is preferablyused since it is thermally stable.

Then, a ligand portion P surrounded by the broken line in the followinggeneral formulae (G1) and (G10) will be described. As described above, Mdenotes an element belonging to Group 9 or Group 10. L represents amonoanionic ligand (specific examples are described below). In addition,n is 2 when M is an element belonging to Group 9, and n is 1 when M isan element belonging to Group 10.

As specific examples of the aromatic hydrocarbon group A, there aresubstituted or unsubstituted 1,2-phenylene group, 1,2-naphthylene group,2-3-naphthylene group, spirofluorene-2,3-diyl group,9,9-dialkylfluorene-2,3-diyl group such as a9,9-dimethylfluorene-2,3-diyl group, and the like. In particular, whenthe organometallic complex of the present invention is evaporated forthe purpose of sublimation, purification, or the like, it is effectiveto use a substituted or unsubstituted 1,2-phenylene group as thearomatic hydrocarbon group A, since the use of the substituted orunsubstituted 1,2-phenylene group can suppress the increase of theevaporation temperature due to the increase of molecular weight. In thecase where the 1,2-phenylene group has a substituent, the substituent isspecifically an alkyl group such as a methyl group, an ethyl group, anisopropyl group, or a tert-butyl group; an alkoxy group such as amethoxy group, an ethoxy group, an isopropoxy group, or a tert-butoxygroup; an aryl group such as a phenyl group or a 4-biphenylyl group; ahalogen group such as a fluoro group; or a trifluoromethyl group. Notethat the unsubstituted 1,2-phenylene group is particularly preferableamong the examples as the aromatic hydrocarbon group A.

As specific examples of the substituent Z, there are various aryl groupssuch as substituted or unsubstituted phenyl group, 1-naphthyl group,2-naphthyl group, spirofluorene-2-yl group, and 9,9-dialkylfluorene-2-ylgroup such as 9,9-dimethylfluorene-2-yl group. In particular, when theorganometallic complex of the present invention is evaporated for thepurpose of sublimation, purification, or the like, it is effective touse a substituted or unsubstituted phenyl group as the substituent Z,since the use of the substituted or unsubstituted phenyl group cansuppress the increase of the evaporation temperature due to the increaseof molecular weight. In the case where the phenyl group has asubstituent, the substituent is specifically an alkyl group such as amethyl group, an ethyl group, an isopropyl group, or a tert-butyl group;an alkoxy group such as a methoxy group, an ethoxy group, an isopropoxygroup, or a tert-butoxy group; an aryl group such as a phenyl group or a4-biphenylyl group; a halogen group such as a fluoro group; or atrifluoromethyl group. In the case where an aryl group is used as thesubstituent Z, an unsubstituted phenyl group is particularly preferableamong the specific examples. The substituent Z may also be an alkylgroup such as a methyl group, an ethyl group, an isopropyl group, atert-butyl group; or an alkoxy group such as a methoxy group, an ethoxygroup, an isopropoxy group, or a tert-butoxy group. Further, thesubstituent Z may also be hydrogen.

As specific examples of the aryl group A_(r) ¹, there are substituted orunsubstituted a phenyl group, a 1-naphthyl group, a 2-naphthyl group, aspirofluorene-2-yl group, a 9,9-dialkylfluorene-2-yl group such as a9,9-dimethylfluorene-2-yl group, and the like. Particularly when asubstituted or unsubstituted phenyl group is used as the aryl groupA_(r) ¹, red-color light emission with excellent color purity and highluminous efficiency (cd/A) can be obtained. In the case where the phenylgroup has a substituent, the substituent may be specifically an alkylgroup such as a methyl group, an ethyl group, an isopropyl group, atert-butyl group; an alkoxy group such as a methoxy group, an ethoxygroup, an isopropoxy group, or a tert-butoxy group; an aryl group suchas a phenyl group or a 4-biphenylyl group; a halogen group such as afluoro group; or a trifluoromethyl group.

In the case where the aromatic hydrocarbon group A is an unsubstituted1,2-phenylene group, an unsubstituted phenyl group, a phenyl groupsubstituted by a fluoro group, or a phenyl group substituted by atrifluoromethyl group is preferably used as the aryl group A_(r) ¹,because red-color light emission with a chromaticity near the redchromaticity defined by NTSC (National Television Standards Committee)(i.e., (x, y)=(0.67, 0.33)) can be obtained.

As specific examples of the substituent R¹, an alkyl groups such as amethyl group, an ethyl group, an isopropyl group, or a tert-butyl group;or an alkoxy group such as a methoxy group, an ethoxy group, anisopropoxy group, or a tert-butoxy group are given. Note that whenhydrogen or a methyl group is used as R¹, steric hindrance of the ligandportion P is reduced and the organometallic complex is easilyortho-metalated with a metal ion, which is preferable in terms of asynthesis yield.

As the structure of the ligand portion P in the above general formulae(G0) and (G10), more specifically, any structure of ligand groups 1 to 9below can be applied. However, the present invention is not limited tothese ligand groups. In the drawings, α denotes a position of carbonwhich is bound to the central metal M. β denotes a position of nitrogenwhich is coordinated to the central metal M.

Next, the monoanionic ligand L in the above general formula (G10) isdescribed. The monoanionic ligand L is preferably either a monoanionicbidentate chelate ligand having a β-diketone structure, a monoanionicbidentate chelate ligand having a carboxyl group, a monoanionicbidentate chelate ligand having a phenolic hydroxyl group, or amonoanionic bidentate chelate ligand in which two ligand elements areboth nitrogen. This is because these ligands have high coordinatingability. More specifically, monoanionic ligands represented by thefollowing structural formulae (L1) to (L8) are given; however, thepresent invention is not limited to these.

By using the central metal M, the ligand groups 1 to 9, the monoanionicligand L as described above in combination as appropriate, anorganometallic complex of the present invention is constituted. Specificstructural formulae (1) to (44) of organometallic complexes of thepresent invention are given below. However, the present invention is notlimited to these.

In the organometallic complexes represented by the above structuralformulae (1) to (44), there can be a geometrical isomer and astereoisomer depending on the type of ligands. The organometalliccomplexes of the present invention include such isomers.

In addition, there are two geometrical isomers of a facial isomer and ameridional isomer in each of the organometallic complexes represented bythe structural formulae (43) and (44). The organometallic complexes ofthe present invention include both isomers, too.

The foregoing organometallic complexes of the present invention can beused as photosensitizers owing to capability of intersystem crossing.Further, it can emit phosphorescence. Thus, the organometallic complexesof the present invention can be used as a light emitting material or alight emitting substance for a light emitting element.

Embodiment Mode 2

Embodiment Mode 2 will describe a mode of a light emitting element whichhas the organometallic complex of the present invention described inEmbodiment Mode 1, as a light emitting substance with reference to FIG.1.

FIG. 1 shows a light emitting element having a light emitting layer 113between a first electrode 101 and a second electrode 102. The lightemitting layer 113 includes the organometallic complex of the presentinvention as described in Embodiment Mode 1.

By applying voltage to such a light emitting element, holes injectedfrom the first electrode 101 side and electrons injected from the secondelectrode 102 side recombine with each other in the light emitting layer113 to bring the organometallic complex of the present invention to anexcited state. When the organometallic complex in the excited statereturns to the ground state, it emits light. As thus described, theorganometallic complex of the present invention functions as a lightemitting substance of the light emitting element. In the light emittingelement of Embodiment Mode 2, the first electrode 101 functions as ananode and the second electrode 102 functions as a cathode.

Here, the light emitting layer 113 includes an organometallic complex ofthe present invention. The light emitting layer 113 is preferably alayer including a substance which has a larger triplet excitation energythan that of the organometallic complex of the present invention as ahost and also including the organometallic complex of the presentinvention which is dispersedly contained as a guest. Thus, quenching oflight emitted from the organometallic complex of the present inventioncaused depending on the concentration can be prevented. It is to benoted that the triplet excitation energy indicates an energy gap betweena ground state and a triplet excited state.

There are no particular limitations on the substance (i.e., a host) usedfor dispersing the organometallic complex of the present invention. Inaddition to a compound having an arylamine skeleton such as2,3-bis(4-diphenylaminophenyl)quinoxaline (abbreviation: TPAQn) or4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB), acarbazole derivative such as 4,4′-di(N-carbazolyl)biphenyl(abbreviation: CBP) or 4,4′,4″-tris(N-carbazolyl)triphenylamine(abbreviation: TCTA), or a metal complex such asbis[2-(2-hydroxyphenyl)pyridinato]zinc (abbreviation: Znpp₂),bis[2-(2-hydroxyphenyl)benzoxazolato]zinc (abbreviation: ZnBOX),bis(2-methyl-8-quinolinolato)(4-phenyphenolato)aluminum (abbreviation:BAlq) or tris(8-quinolinolato)aluminum (abbreviation: Alq₃) ispreferably used. Moreover, a high molecular compound such aspoly(N-vinylcarbazole) (abbreviation: PVK) can also be used. Inparticular when using a metal complex such asbis[2-(2-hydroxyphenyl)pyridinato]zinc (abbreviation: Znpp₂),bis[2-(2-hydroxyphenyl)benzoxazolato]zinc (abbreviation: ZNBOX), orbis(2-methyl-8-quinolinolato)(4-phenyphenolato)aluminum (abbreviation:BAlq), the organometallic complex of the present invention can emitlight efficiently. It is further preferable to use a zinc oxide.

Since the organometallic complex of the present invention can emit redlight, a light emitting element which emits red light can be provided.Since the organometallic complex of the present invention has high lightemission efficiency, a light emitting element with high light emissionefficiency can be provided. Furthermore, a light emitting element whichemits red light with high luminous efficiency (cd/A) can be provided.

Since the light emitting element of the present invention has high lightemission efficiency, power consumption can be reduced.

Although there are no particular limitations on the first electrode 101,the first electrode 101 is preferably formed of a substance which has ahigh work function when the first electrode 101 functions as an anode asin Embodiment Mode 2. Specifically, in addition to indium tin oxide(ITO), indium tin oxide containing silicon oxide (ITSO), and indiumoxide containing zinc oxide at 2 to 20 wt % (IZO), gold (Au), platinum(Pt), nickel (Ni), tungsten (W), chromium (Cr), molybdenum (Mo), iron(Fe), cobalt (Co), copper (Cu), palladium (Pd), or the like can be used.The first electrode 101 can be formed by, for example, a sputteringmethod, an evaporation method, or the like.

Further, although there are not particular limitations on the secondelectrode 102, the second electrode 102 is preferably formed of asubstance which has a low work function when the second electrode 102functions as a cathode as in Embodiment Mode 2. Specifically, inaddition to aluminum (Al) or indium (In), an alkali metal such aslithium (Li) or cesium (Cs); an alkaline-earth metal such as magnesium(Mg) or calcium (Ca); a rare-earth metal such as erbium (Er) orytterbium (Yb) can be used. In addition, an alloy such asaluminum-lithium alloy (AlLi) or magnesium-silver alloy (MgAg) can alsobe used. The second electrode 102 can be formed by, for example, asputtering method, an evaporation method, or the like.

In order to extract emitted light to the outside, one or both of thefirst electrode 101 and the second electrode 102 is/are preferably anelectrode formed of a conductive film of indium tin oxide (ITO) or thelike which can transmit visible light or an electrode with a thicknessof several to several tens of nm so as to transmit visible light.

In addition, a hole transporting layer 112 may be provided between thefirst electrode 101 and the light emitting layer 113 as shown in FIG. 1.Here, the hole transporting layer is a layer which has a function oftransporting holes injected from the first electrode 101 to the lightemitting layer 113. The hole transporting layer 112 is provided to keepthe first electrode 101 away from the light emitting layer 113 in thisway; thus, quenching of light due to a metal can be prevented. However,the hole transporting layer 112 is not necessarily provided.

There are no particular limitations on a substance forming the holetransporting layer 112, and typically, an aromatic amine compound suchas 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB),4,4′-bis[N-(3-methylphenyl)-N-phenylamino]biphenyl (abbreviation: TPD),4,4′-bis[N-(9,9-dimethylfluoren-2-yl)-N-phenylamino]biphenyl(abbreviation: DFLDPBi), 4,4′,4″-tris(N,N-diphenylamino)triphenylamine(abbreviation: TDATA), or4,4′,4″-tris[N-(3-methylphenyl)-N-phenylamino]triphenylamine(abbreviation: m-MTDATA) can be used. Moreover, a high molecularcompound such as poly(4-vinyl triphenylamine) (abbreviation: PVTPA) canalso be used.

In addition, the hole transporting layer 112 may have a multilayerstructure in which two or more layers are stacked, or may be formed of amixture of two or more substances.

Further, an electron transporting layer 114 may be provided between thesecond electrode 102 and the light emitting layer 113 as shown inFIG. 1. Here, the electron transporting layer is a layer which has afunction of transporting electrons injected from the second electrode102 to the light emitting layer 113. The electron transporting layer 114is provided to keep the second electrode 102 away from the lightemitting layer 113 in this way; thus, quenching of light due to a metalcan be prevented. Note that the electron transporting layer 114 is notnecessarily provided.

There are no particular limitations on a substance forming the electrontransporting layer 114. Typically, a metal complex such astris(8-quinolinolato)aluminum (abbreviation: Alq₃),tris(4-methyl-8-quinolinolato)aluminum (abbreviation: Almq₃),bis(10-hydroxybenzo[h]quinolinato)beryllium (abbreviation: BeBq₂),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation:BAlq), bis[2-(2-hydroxyphenyl)benzoxazolato]zinc (abbreviation: ZnBOX),or bis[2-(2-hydroxyphenyl)benzothiazolato]zinc (abbreviation: Zn(BTZ)₂)may be used. Further, a heteroaromatic compound such as2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (abbreviation:PBD), 1,3-bis[5-(p-tert-butylphenyl)-1,3,4-oxadiazol-2-yl]benzene(abbreviation: OXD-7),3-(4-tert-butylphenyl)-4-phenyl-5-(4-biphenylyl)-1,2,4-triazole(abbreviation: TAZ),3-(4-tert-butylphenyl)-4-(4-ethylphenyl)-5-(4-biphenylyl)-1,2,4-triazole(abbreviation: p-EtTAZ), bathophenanthroline (abbreviation: BPhen),bathocuproin (abbreviation: BCP), or4,4′-bis(5-methylbenzoxazol-2-yl)stilbene (abbreviation: BzOs) can alsobe used. In addition, a high molecular compound such aspoly(2,5-pyridine-diyl) (abbreviation: PPy) can also be used.

In addition, the electron transporting layer 114 may have a multilayerstructure in which two or more layers are stacked, or may be formed of amixture of two or more substances.

Further, a hole injecting layer 111 may be provided between the firstelectrode 101 and the hole transporting layer 112 as shown in FIG. 1.Here, the hole injecting layer is a layer that has a function ofassisting injection of holes from an electrode functioning as an anodeto the hole transporting layer 112. Note that the hole injecting layer111 is not necessarily provided.

There are no particular limitations on a substance forming the holeinjecting layer 111. For forming the hole injecting layer 111, a metaloxide such as vanadium oxide (VO_(x)), niobium oxide (NbO_(x)), tantalumoxide (TaO_(x)), chromium oxide (CrO_(x)), molybdenum oxide (MoO_(x)),tungsten oxide (WO_(x)), manganese oxide (MnO_(x)), rhenium oxide(ReO_(x)), or ruthenium oxide (RuO_(x)) can be used. In addition, aphthalocyanine based compound such as phthalocyanine (abbreviation:H₂Pc) or copper phthalocyanine (abbreviation: CuPc) can also be used. Inaddition, the substances for forming the hole transporting layer 112 asdescribed above can also be used. Further, a high molecular compoundsuch as a mixture of poly(ethylenedioxythiophene) and poly(styrenesulfonate) (abbreviation: (PEDOT/PSS)) can also be used.

A composite material which is formed by combining an organic compoundand an electron acceptor may be used for the hole injecting layer 111.The composite material is superior in a hole injecting property and ahole transporting property, since holes are generated in the organiccompound by the electron acceptor. In this case, the organic compound ispreferably a material excellent in transporting the generated holes.Specifically, the foregoing substances for forming the hole transportinglayer 112 (such as aromatic amine compound) can be used for example. Inaddition, as the electron acceptor, a substance showing an electronaccepting property to an organic compound may be used, and specifically,a transition metal oxide is preferable. For example, vanadium oxide(VO_(x)), niobium oxide (NbO_(x)), tantalum oxide (TaO_(x)), chromiumoxide (CrO_(x)), molybdenum oxide (MoO_(x)), tungsten oxide (WO_(x)),manganese oxide (MnO_(x)), rhenium oxide (ReO_(x)), ruthenium oxide(RuO_(x)) and the like are given. Lewis acid such as iron chloride(III)or aluminum chloride(III) can also be used. In addition, an organiccompound such as 7,7,8,8-tetracyano-2,3,5,6-tetrafluoroquinodimethane(abbreviation: F4-TCNQ) can also be used.

The hole injecting layer 111 may have a multilayer structure in whichtwo or more layers are stacked, or may be formed of a mixture of two ormore substances.

Further, an electron injecting layer 115 may be provided between thesecond electrode 102 and the electron transporting layer 114 as shown inFIG. 1. Here, the electron injecting layer is a layer which has afunction of assisting injection of electrons from the electrodefunctioning as a cathode to the electron transporting layer 114. It isto be noted that the electron injecting layer 115 is not necessarilyprovided.

There are no particular limitations on a substance forming the electroninjecting layer 115. A compound of an alkali metal or an alkaline-earthmetal such as lithium fluoride (LiF), cesium fluoride (CsF), calciumfluoride (CaF₂), lithium oxide (LiO_(x)) can be used. In addition, arare-earth metal compound such as erbium fluoride (ErF₃) can also beused. The above-mentioned substances for forming the electrontransporting layer 114 can also be used.

A composite material which is formed by combining an organic compoundand an electron donor may be used for the electron injecting layer 115.The composite material is superior in an electron injecting property andan electron transporting property, since electrons are generated in theorganic compound by the electron donor. In this case, the organiccompound is preferably a material excellent in transporting thegenerated electrons. Specifically, the foregoing materials for formingthe electron transporting layer 114 (such as a metal complex, aheteroaromatic compound or the like) can be used for example. As theelectron donor, a substance showing an electron donating property to theorganic compound may be used, and specifically an alkali metal, analkaline-earth metal or a rare-earth metal, for example, lithium,cesium, magnesium, calcium, erbium, or ytterbium, is preferable.Further, an alkali metal oxide, or an alkaline-earth metal oxide ispreferable, and for example, lithium oxide (LiO_(x)), calcium oxide(CaO_(x)), barium oxide (BaO_(x)), or the like can be given. Lewis acidsuch as magnesium oxide can also be used. In addition, an organiccompound such as tetrathiafulvalene (abbreviation: TTF) can also beused.

In the foregoing light emitting element of the present invention, eachof the hole injecting layer 111, the hole transporting layer 112, thelight emitting layer 113, the electron transporting layer 114, and theelectron injecting layer 115 may be formed by any method, for example,an evaporation method, an inkjet method, an application method, or thelike. In addition, the first electrode 101 or the second electrode 102may also be formed by any method, for example, a sputtering method, anevaporation method, an inkjet method, an application method, or thelike.

Embodiment Mode 3

The light emitting element of the present invention may have a pluralityof light emitting layers. A plurality of light emitting layers areprovided and lights emitted from each of the light emitting layers aremixed, thereby obtaining light which is the combination of the pluralityof light. Accordingly, white-color light can be obtained for example. InEmbodiment Mode 3, a light emitting element having a plurality of lightemitting layers is described with reference to FIG. 2.

In FIG. 2, a first light emitting layer 213 and a second light emittinglayer 215 are provided between a first electrode 201 and a secondelectrode 202. Light in which light emitted from the first lightemitting layer 213 and light emitted from the second light emittinglayer 215 are mixed can be obtained. A separation layer 214 ispreferably formed between the first light emitting layer 213 and thesecond light emitting layer 215.

When voltage is applied so that the potential of the first electrode 201is higher than the potential of the second electrode 202, current flowsbetween the first electrode 201 and the second electrode 202, and holesand electrons are recombined in the first light emitting layer 213, thesecond light emitting layer 215, or the separation layer 214. Generatedexcitation energy is distributed to the first light emitting layer 213and the second light emitting layer 215 to bring each of a first lightemitting substance contained in the first light emitting layer 213 and asecond light emitting substance contained in the second light emittinglayer 215 to an excited state. Then, the first and second light emittingsubstances in the excited state emit light when returning to the groundstate.

The first light emitting layer 213 contains the first light emittingsubstance typified by a fluorescent compound such as perylene,2,5,8,11-tetra(tert-butyl)perylene (abbreviation: TBP),4,4′-bis(2,2-diphenylvinyl)biphenyl (abbreviation: DPVBi),4,4′-bis[2-(N-ethylcarbazol-3-yl)vinyl]biphenyl (abbreviation: BCzVBi),bis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation:BAlq), or bis(2-methyl-8-quinolinolato)galliumchloride (abbreviation:Gamq₂Cl); or a phosphorescent compound such asbis{2-[3,5-bis(trifluoromethyl)phenyl]pyridinato-N,C^(2′)}iridium(III)picolinate(abbreviation: Ir(CF₃ ppy)₂(pic)),bis[2-(4,6-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)acetylacetonate(abbreviation: FIr(acac)),bis[2-(4,6-difluorophenyl)pyridinato-N,C^(2′)]iridium(III)picolinate(abbreviation: FIrpic), orbis[2-(4,6-difuluorophenyl)pyridinato-N,C^(2′)]iridium(III)tetra(1-pyrazolyl)borate(abbreviation: FIr6), from which light emission with a peak at 450 to510 nm in an emission spectrum (i.e., blue light to blue green light)can be obtained. In addition, when the first light emitting substance isa fluorescent compound, the first light emitting layer 213 maypreferably have a structure in which a substance having a larger singletexcitation energy than the first light emitting substance is used as afirst host and the first light emitting substance is dispersedlycontained as a guest. Further, when the first light emitting substanceis a phosphorescent compound, the light emitting layer 213 preferablyhas a structure in which a substance having a larger triplet excitationenergy than the first light emitting substance is used as a first hostand the first light emitting substance is dispersedly contained as aguest. As the first host, 9,10-di(2-naphthyl)anthracene (abbreviation:DNA), 2-tert-butyl-9,10-di(2-naphthyl)anthracene (abbreviation: t-BuDNA)or the like can be used as well as NPB, CBP, TCTA, or the like. It isnoted that the singlet excitation energy is an energy difference betweena ground state. In addition, a singlet excited state. and the tripletexcitation energy is an energy difference between a ground state and atriplet excited state.

On the other hand, the second light emitting layer 215 includes anorganometallic complex of the present invention and can exhibit lightemission of red color. Further, since the organometallic complex of thepresent invention has high light emission efficiency, a light emittingelement with high luminous efficiency can be obtained. In addition, alight emitting element with reduced power consumption can be obtained.

The second light emitting layer 215 may have a similar structure to thelight emitting layer 113 described in Embodiment Mode 2.

In addition, the separation layer 214 can be specifically formed ofTPAQn, NPB, CBP, TCTA, Znpp₂, ZnBOX or the like described above. In thisway, by providing the separation layer 214, a defect that emissionintensity of one of the first light emitting layer 213 and the secondlight emitting layer 215 is stronger than the other can be prevented.Note that the separation layer 214 is not necessarily provided, and itmay be provided as appropriate such that the ratio in emission intensityof the first light emitting layer 213 and the second light emittinglayer 215 can be adjusted.

In Embodiment Mode 3, an organometallic complex of the present inventionis used for the second light emitting layer 215, and another lightemitting substance is used for the first light emitting layer 213;however, the organometallic complex of the present invention may be usedfor the first light emitting layer 213, and another light emittingsubstance may be used for the second light emitting layer 215.

In Embodiment Mode 3, a light emitting element including two lightemitting layers is described as shown in FIG. 2; however, the number ofthe light emitting layers is not limited to two, and may be three, forexample. Light emission from each light emitting layer may be mixed. Asa result, white-color emission can be obtained, for example.

In addition, the first electrode 201 may have a similar structure to thefirst electrode 101 described in Embodiment Mode 2. In addition, thesecond electrode 202 may have a similar structure to the secondelectrode 102 described in Embodiment Mode 2.

In Embodiment Mode 3, as shown in FIG. 2, the hole injecting layer 211,the hole transporting layer 212, the electron transporting layer 216,and the electron injecting layer 217 are provided. As to structures ofthese layers, the structures of the respective layers described inEmbodiment Mode 2 may be applied. However, these layers are notnecessarily provided and may be provided depending on the elementcharacteristics.

Embodiment Mode 4

Embodiment Mode 4 exemplifies a light emitting element which includes aplurality of light emitting layers, which has a different elementstructure from that in Embodiment Mode 3, and in which light is emittedfrom each light emitting layer. Therefore, also in Embodiment Mode 4,light which is the combination of a plurality of light can be obtained.In other words, white-color light can be obtained, for example.Hereinafter, description is made with reference to FIG. 3.

In the light emitting element of FIG. 3, a first light emitting layer313 and a second light emitting layer 323 are provided between a firstelectrode 301 and a second electrode 302. An N layer 315 and a P layer321 as charge generating layers are provided between the first lightemitting layer 313 and the second light emitting layer 323.

The N layer 315 is a layer for generating electrons, and the P layer 321is a layer for generating holes. When voltage is applied such that thepotential of the first electrode 301 is higher than that of the secondelectrode 302, holes injected from the first electrode 301 and electronsinjected from the N layer 315 are recombined in the first light emittinglayer 313, and thus, a first light emitting substance included in thefirst light emitting layer 313 emits light. Further, electrons injectedfrom the second electrode 302 and holes injected from the P layer 321are recombined in the second light emitting layer 323, and thus, asecond light emitting substance included in the second light emittinglayer 323 emits light.

The first light emitting layer 313 may have a similar structure to thefirst light emitting layer 213 of Embodiment Mode 3, and light with apeak of emission spectrum in 450 nm to 510 nm (i.e., blue light to bluegreen light) can be emitted. The second light emitting layer 323 mayhave a similar structure to the second light emitting layer 215 ofEmbodiment Mode 3, and includes an organometallic complex of the presentinvention, and red light can be obtained. Since the organometalliccomplex of the present invention has high luminous efficiency, a lightemitting element with high light emission efficiency can be obtained.Further, a light emitting element with reduced power consumption can beobtained.

Since the N layer 315 is a layer for generating electrons, it may beformed using a composite material in which the organic compound and theelectron donor described in Embodiment Mode 2 are combined. By employingsuch a structure, electrons can be injected to the first light emittinglayer 313 side.

Since the P layer 321 is a layer for generating holes, it may be formedusing a composite material in which the organic compound and theelectron donor described in Embodiment Mode 2 are combined. By employingsuch a structure, holes can be injected to the second light emittinglayer 323 side. For the P layer 321, a metal oxide having an excellenthole injecting property, such as MoO_(x), VO_(x), ITO, or ITSO can beused.

Here, Embodiment Mode 4 describes a light emitting element in which thetwo light emitting layers are provided as shown in FIG. 3; however, thenumber of light emitting layers is not limited to two. For example, thenumber may be three as long as light from each light emitting layer aremixed. Consequently, white-color light can be obtained for example.

The first electrode 301 may have a similar structure to the firstelectrode 101 of Embodiment Mode 2. In addition, the second electrode302 may have a similar structure to the second electrode 102 describedin Embodiment Mode 2.

In Embodiment Mode 4, as shown in FIG. 3, a hole injecting layer 311,hole transporting layers 312 and 322, electron transporting layers 314and 324, and an electron injecting layer 325 are provided. As to theselayer structures, the structures of the respective layers described inEmbodiment Mode 2 may also be applied. Note that these layers may beprovided as appropriate depending on the element characteristics, sincethese layers are not necessarily provided.

Embodiment Mode 5

A mode of a light emitting element using the organometallic complex ofthe present invention as a sensitizer will be described with referenceto FIG. 1.

FIG. 1 shows the light emitting element having the light emitting layer113 between the first electrode 101 and the second electrode 102. Thelight emitting layer 113 contains the organometallic complex of thepresent invention described in Embodiment Mode 1, and a fluorescentcompound which can emit light with a longer wavelength than theorganometallic complex of the present invention.

In the light emitting element like this, holes injected from the firstelectrode 101 and electrons injected from the second electrode 102 arerecombined in the light emitting layer 113 to bring the fluorescentcompound to an excited state. Then, light is emitted when thefluorescent compound in the excited state returns to the ground state.In this case, the organometallic complex of the present invention actsas a sensitizer for the fluorescent compound to make more molecules ofthe fluorescent compound be in the singlet excited state. In thismanner, a light emitting element with excellent light emissionefficiency can be obtained by using the organometallic complex of thepresent invention as a sensitizer. It is to be noted that the firstelectrode 101 functions as an anode and the second electrode 102functions as a cathode in the light emitting element of Embodiment Mode5.

Here, the light emitting layer 113 includes an organometallic complex ofthe present invention, and a fluorescent compound which can emit lightwith a longer wavelength than the organometallic complex of the presentinvention. The light emitting layer 113 may preferably have a structurein which a substance having a larger singlet excitation energy than thefluorescent compound as well as a substance having a larger tripletexcitation energy than the organometallic complex of the presentinvention is used as a host, and the organometallic complex of thepresent invention and the fluorescent compound are dispersedly containedas a guest.

There are no particular limitations on a substance (i.e., host) used fordispersing the organometallic complex of the present invention and thefluorescent compound, and a substance which is used as a host inEmbodiment Mode 2, or the like can be used.

In addition, there are also no particular limitations on the fluorescentcompound; however, a compound which can exhibit emission of red light toinfrared light, such as4-dicyanomethylene-2-isopropyl-6-[2-(1,1,7,7-tetramethyljulolidin-9-yl)ethenyl]-4H-pyran (abbreviation: DCJTI), magnesium phthalocyanine, magnesiumporphyrin, phthalocyanine or the like, is preferable.

Note that the first electrode 101 and the second electrode 102 may bothhave similar structures to the first electrode and the second electrodeof Embodiment Mode 2, respectively.

In Embodiment Mode 5, as shown in FIG. 1, the hole injecting layer 111,the hole transporting layer 112, the electron transporting layer 114,and the electron injecting layer 115 are provided. As to these layersalso, the structures of the respective layers described in EmbodimentMode 2 may be applied. Note that these layers may be provided asappropriate depending on the element characteristics, since these layersare not necessarily provided.

The foregoing light emitting element can emit light highly efficientlyby using the organometallic complex of the present invention as asensitizer.

Embodiment Mode 6

In Embodiment Mode 6, a light emitting device manufactured using anorganometallic complex of the present invention will be described.

In this embodiment mode, a light emitting device manufactured using anorganometallic complex of the present invention will be described withreference to FIGS. 4A and 4B. It is to be noted that FIG. 4A is a topview of a light emitting device and FIG. 4B is a cross sectional view ofFIG. 4A taken along lines A-A′ and B-B′. Reference numeral 601 denotes adriver circuit portion (source side driver circuit); 602 denotes a pixelportion; and 603 denotes a driver circuit portion (gate side drivercircuit), which are indicated by dotted lines. Reference numeral 604denotes a sealing substrate; 605 denotes a sealing material; and aportion surrounded by the sealing material 605 is a space 607.

In addition, a lead wiring 608 is a wiring for transmitting a signal tobe inputted to the source side driver circuit 601 and the gate sidedriver circuit 603 and receives a video signal, a clock signal, a startsignal, a reset signal, and the like from an FPC (flexible printedcircuit) 609, which is an external input terminal. Note that only theFPC is shown here; however, the FPC may be provided with a printedwiring board (PWB). The light emitting device in this specificationincludes not only a light emitting device itself but also a lightemitting device attached with an FPC or a PWB.

Next, a cross-sectional structure is described with reference to FIG.4B. Although the driver circuit portion and the pixel portion are formedover an element substrate 610, the source side driver circuit 601 whichis the driver circuit portion and one pixel in the pixel portion 602 areshown here.

A CMOS circuit, which has a combination of an n-channel TFT 623 and ap-channel TFT 624, is formed as the source side driver circuit 601. Thedriver circuit may be formed using various circuits such as a CMOScircuit, a PMOS circuit, or an NMOS circuit. Although a driverintegration type in which a driver circuit is formed over a substrate isdescribed in this embodiment mode, a driver circuit is not necessarilyformed over a substrate and can be formed outside a substrate.

Further, the pixel portion 602 has a plurality of pixels, each of whichincludes a switching TFT 611, a current control TFT 612, and a firstelectrode 613 which is electrically connected to the drain of thecurrent control TFT 612. Note that an insulator 614 is formed so as tocover an end portion of the first electrode 613. Here, a positivephotosensitive acrylic resin film is used for the insulator 614.

The insulator 614 is formed so as to have a curved surface havingcurvature at an upper end portion or a lower end portion thereof inorder to make the coverage favorable. For example, in the case of usinga positive photosensitive acrylic resin as a material for the insulator614, the insulator 614 is preferably formed so as to have a curvedsurface with a curvature radius (0.2 μm to 3 μm) only at the upper endportion thereof. Either a negative type which becomes insoluble in anetchant by light irradiation or a positive type which becomes soluble inan etchant by light irradiation can be used as the insulator 614.

A layer 616 containing a light emitting substance and a second electrode617 are formed over the first electrode 613. Here, a material having ahigh work function is preferably used as a material for the firstelectrode 613, which serves as an anode. For example, the firstelectrode 613 can be formed with the used of stacked layers of atitanium nitride film and a film containing aluminum as its maincomponent; a three-layer structure of a titanium nitride film, a filmcontaining aluminum as its main component, and another titanium nitridefilm; or the like as well as a single-layer film such as an ITO film, anindium tin oxide film containing silicon, an indium oxide filmcontaining zinc oxide of 2 to 20 wt %, a titanium nitride film, achromium film, a tungsten film, a Zn film, or a Pt film. When the firstelectrode 613 has a stacked layer structure, it can have low resistanceas wiring and form a favorable ohmic contact. Further, the firstelectrode 613 can function as an anode.

In addition, the layer 616 containing a light emitting substance isformed by various methods such as an evaporation method using anevaporation mask, an ink-jet method, and a spin coating method. Thelayer 616 containing a light emitting substance has the organometalliccomplex of the present invention described in Embodiment Mode 1.Further, the layer 616 containing a light emitting substance may includeanother material such as a low molecular material, a medium molecularmaterial (including an oligomer and a dendrimer), or a high molecularmaterial.

As a material used for the second electrode 617, which is formed overthe layer 616 containing a light emitting substance and serves as acathode, a material having a low work function (Al, Mg, Li, Ca, or analloy or a compound of them such as MgAg, MgIn, AlLi, LiF, or CaF₂) ispreferably used. In the case where light generated in the layer 616containing a light emitting substance is transmitted through the secondelectrode 617, stacked layers of a metal thin film and alight-transmissive conductive film (of ITO, indium oxide containing zincoxide of 2 to 20 wt %, indium tin oxide containing silicon, zinc oxide(ZnO), or the like) are preferably used as the second electrode 617.

By attaching the sealing substrate 604 to the element substrate 610 withthe sealing material 605, a light emitting element 618 is provided inthe space 607 surrounded by the element substrate 610, the sealingsubstrate 604, and the sealing material 605. It is to be noted that thespace 607 is filled with a filler. There is a case where the space 607is filled with the sealing material 605 as well as an inert gas(nitrogen, argon, or the like).

It is to be noted that an epoxy-based resin is preferably used as thesealing material 605. The material desirably allows as little moistureand oxygen as possible to penetrate. As the sealing substrate 604, aplastic substrate made of FRP (Fiberglass-Reinforced Plastics), PVF(polyvinyl fluoride), polyester, acrylic, or the like can be usedbesides a glass substrate or a quartz substrate.

In the above-described manner, a light emitting device manufacturedusing the organometallic complex of the present invention can beobtained.

A light emitting device of the present invention can have favorablecharacteristics since the organometallic complex described in EmbodimentMode 1 is used for the light emitting device. Specifically, since thelight emitting element with high light emission efficiency is included,a light emitting device with reduced power consumption can be obtained.Further, since light emission of red color with high luminous efficiencycan be realized, a light emitting device with reduced power consumptionand excellent color reproductivity, which is suitable for a full-colordisplay, can be obtained.

In this embodiment mode, description is made of an active light emittingdevice for controlling driving of a light emitting element with atransistor. Alternatively, a passive light emitting device which drivesa light emitting element without particularly providing an element fordriving such as a transistor may also be used. FIG. 5 shows aperspective view of a passive light emitting device which ismanufactured by using the present invention. In FIG. 5, a layer 955containing a light emitting substance is provided between an electrode952 and an electrode 956 over a substrate 951. An edge portion of theelectrode 952 is covered with an insulating layer 953. Then, a partitionlayer 954 is provided over the insulating layer 953. Side walls of thepartition layer 954 slope so that a distance between one side wall andthe other side wall becomes narrower toward a substrate surface. Inother words, a cross section of the partition layer 954 in the directionof a short side is trapezoidal, and a base (side which is provided inthe same direction as a plane direction of the insulating layer 953 andin contact with the insulating layer 953) is shorter than an upper side(side which is provided in the same direction as the plane direction ofthe insulating layer 953 and not in contact with the insulating layer953). By providing the partition layer 954 in this manner, a defect ofthe light emitting element due to static electricity or the like can beprevented. In addition, the passive light emitting device can also bedriven with low power consumption when it includes the light emittingelement having high light emission efficiency of the present invention.

Embodiment Mode 7

In Embodiment Mode 7, an electronic device of the present inventionincluding the light emitting device described in Embodiment Mode 6 as apart will be described. The electronic device of the present inventionincluding the organometallic complex described in Embodiment Mode 1 hasa display portion with high light emission efficiency and reduced powerconsumption. Further, it also includes a display portion with excellentcolor reproductivity. In the case where the organometallic complex ofthe present invention is used for a full-color display, various lightemitting substances can be used for a light emitting element of a colorother than red color and a light emitting element having a similarstructure to that described in Embodiment Modes 2 to 5 can be employed.

As an electronic device including a light emitting element manufacturedusing the organometallic complex of the present invention, a camera suchas a video camera or a digital camera, a goggle type display, anavigation system, an audio reproducing device (car audio componentstereo, audio component stereo, or the like), a computer, a gamemachine, a portable information terminal (mobile computer, mobile phone,portable game machine, electronic book, or the like), and an imagereproducing device provided with a recording medium (specifically, adevice capable of reproducing a recording medium such as a DigitalVersatile Disc (DVD) and provided with a display device that can displaythe image), and the like are given. Specific examples of theseelectronic device are shown in FIGS. 6A to 6D.

FIG. 6A shows a television device according to the present invention,which includes a housing 9101, a supporting base 9102, a display portion9103, a speaker portion 9104, a video input terminal 9105, and the like.In the television device, the display portion 9103 has light emittingelements similar to those described in Embodiment Modes 2 to 5, whichare arranged in matrix. One feature of the light emitting element isthat high light emission efficiency and low power consumption arepossible. In addition, light emission of red color with high luminousefficiency can be realized. The display portion 9103 which includes thelight emitting elements has similar features. Therefore, in thetelevision device, image quality is hardly deteriorated and low powerconsumption is achieved. With such features, deterioration compensationfunctions and power supply circuits can be significantly reduced ordownsized in the television device; therefore, small size andlightweight housing 9101 and supporting base 9102 can be achieved. Inthe television device according to the present invention, low powerconsumption, high image quality, and small size and lightweight areachieved; therefore, a product which is suitable for any residentialenvironment can be provided. Further, since the light emitting elementcapable of emitting red light with high luminous efficiency is included,a television device having a display portion with low power consumptionand excellent color reproductivity can be obtained.

FIG. 6B shows a computer according to the present invention, whichincludes a main body 9201, a housing 9202, a display portion 9203, akeyboard 9204, an external connection port 9205, a pointing mouse 9206,and the like. In the computer, the display portion 9203 has lightemitting elements similar to those described in Embodiment Modes 2 to 5,which are arranged in matrix. One feature of the light emitting elementis that high light emission efficiency and low power consumption arepossible. In addition, light emission of red color with high luminousefficiency can be realized. The display portion 9203 which includes thelight emitting elements has similar features. Therefore, in thecomputer, image quality is hardly deteriorated and lower powerconsumption is achieved. With such features, deterioration compensationfunctions and power supply circuits can be significantly reduced ordownsized in the computer; therefore, small size and lightweight mainbody 9201 and housing 9202 can be achieved. In the computer according tothe present invention, low power consumption, high image quality, andsmall size and lightweight are achieved; therefore, a product which issuitable for any residential environment can be provided. Further, sincethe light emitting element capable of emitting red light with highluminous efficiency is included, a computer having a display portionwith low power consumption and excellent color reproductivity can beobtained.

FIG. 6C shows a mobile phone according to the present invention, whichincludes a main body 9401, a housing 9402, a display portion 9403, anaudio input portion 9404, an audio output portion 9405, an operation key9406, an external connection port 9407, an antenna 9408, and the like.In the mobile phone, the display portion 9403 has light emittingelements similar to those described in Embodiment Modes 2 to 5, whichare arranged in matrix. One feature of the light emitting element isthat high light emission efficiency and low power consumption arepossible. In addition, light emission of red color with high luminousefficiency can be realized. The display portion 9403 which includes thelight emitting elements has similar features. Therefore, in the mobilephone, image quality is hardly deteriorated and lower power consumptionis achieved. With such features, deterioration compensation functionsand power supply circuits can be significantly reduced or downsized inthe mobile phone; therefore, small size and lightweight main body 9401and the housing 9402 can be achieved. In the mobile phone according tothe present invention, low power consumption, high image quality, andsmall size and lightweight are achieved; therefore, a production whichis suitable for carrying can be provided. Further, since the lightemitting element capable of emitting red light with high luminousefficiency is included, a mobile phone having a display portion with lowpower consumption and excellent color reproductivity can be obtained.

FIG. 6D shows a camera according to the present invention, whichincludes a main body 9501, a display portion 9502, a housing 9503, anexternal connection port 9504, a remote control receiving portion 9505,an image receiving portion 9506, a battery 9507, an audio input portion9508, operation keys 9509, an eye piece portion 9510, and the like. Inthis camera, the display portion 9502 has light emitting elementssimilar to those described in Embodiment Modes 2 to 5, which arearranged in matrix. One feature of the light emitting element is thathigh light emission efficiency and low power consumption are possible.In addition, light emission of red color with high luminous efficiencycan be realized. The display portion 9502 which includes the lightemitting elements has similar features. Therefore, in the camera, imagequality is hardly deteriorated and lower power consumption can beachieved. With such features, deterioration compensation functions andpower supply circuits can be significantly reduced or downsized in thecamera; therefore, small size and lightweight main body 9501 can beachieved. In the camera according to the present invention, low powerconsumption, high image quality, and small size and lightweight areachieved; therefore, a product which is suitable for carrying can beprovided. Further, since the light emitting element capable of emittingred light with high luminous efficiency is included, a camera having adisplay portion with low power consumption and excellent colorreproductivity can be obtained.

As described above, the applicable range of the light emitting device ofthe present invention is so wide that the light emitting device can beapplied to electronic devices in various fields. By using theorganometallic complex of the present invention, electronic deviceswhich have display portions consuming low power and having excellentcolor reproductivity can be provided.

The light emitting device of the present invention can also be used as alighting device. One mode using the light emitting element of thepresent invention as the lighting device is described with reference toFIG. 7.

FIG. 7 shows an example of a liquid crystal display device using thelight emitting device of the present invention as a backlight. Theliquid crystal display device shown in FIG. 7 includes a housing 901, aliquid crystal layer 902, a backlight 903, and a housing 904, and theliquid crystal layer 902 is connected to a driver IC 905. The lightemitting device of the present invention is used for the backlight 903,and current is supplied through a terminal 906.

By using the light emitting device of the present invention as thebacklight of the liquid crystal display device, a backlight with reducedpower consumption can be obtained. The light emitting device of thepresent invention is a lighting device with plane light emission, andcan have a large area. Therefore, the backlight can have a large area,and a liquid crystal display device having a large area can be realized.Furthermore, the light emitting device of the present invention has athin shape and consumes low power; therefore, a thin shape and low powerconsumption of a display device can also be achieved.

FIG. 8 shows an example of using the light emitting device to which thepresent invention is applied as a table lamp, which is a lightingdevice. A table lamp shown in FIG. 8 has a chassis 2001 and a lightsource 2002, and the light emitting device of the present invention isused as the light source 2002. The light emitting device of the presentinvention can emit light with high luminance; therefore, in such a casewhere fine manipulation is performed, the manipulator's hand can bebrightly lighted.

FIG. 9 shows an example of using the light emitting device to which thepresent invention is applied as an indoor lighting device 3001. Sincethe light emitting device of the present invention can have a largearea, the light emitting device of the present invention can be used asa lighting device having a large area. Further, the light emittingdevice of the present invention has a thin shape and consumes low power;therefore, the light emitting device of the present invention can beused as a lighting device having a thin shape and consuming low power. Atelevision device relating to the present invention as shown in FIG. 6Ais placed in a room where the light emitting device to which the presentinvention is applied is used as the indoor lighting device 3001. Thus,public broadcasting and movies can be watched. In such a case, sinceboth of the devices consume low power, a powerful image can be watchedin a bright room without concern about electricity charges.

Example 1

<Synthetic Example 1 >

In Synthetic Example 1, a synthetic example of an organometallic complexof the present invention represented by structural formula (1) inEmbodiment Mode 1,(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: [Ir(tppr)₂(acac)]), will be specifically described.

<Step 1: Synthesis of 2,3,5-triphenylpyrazine (abbreviation: Htppr)>

First, in a nitrogen atmosphere, 5.5 mL of a dibutyl ether solutioncontaining phenyl lithium (produced by Wako Pure Chemical Industries,Ltd., 2.1 mol/L) and 50 mL of diethylether were mixed to prepare asolution. Then, 2.43 g of 2,3-diphenylpyrazine was dropped into thissolution while the solution was being cooled with ice, and stirred at aroom temperature for 24 hours. After the stirring, water was added intothe mixture and an organic layer was extracted with diethylether. Theextracted organic layer washed with water and dried with magnesiumsulfate. After the drying, the organic layer was added with activatedmanganese dioxide excessively, mixed sufficiently, and then filtered. Asolvent of the filtrate was distilled off, and a residue obtained wasrecrystallized with ethanol so that a pyrazine derivative, Htppr (yellowpowder, yield of 56%), was obtained. A synthetic scheme of Step 1 isshown in the following (a-1).

<Step 2: Synthesis ofdi-μ-chloro-bis[bis(2,3,5-triphenylpyrazinato)iridium(III)](abbreviation:[Ir(tppr)₂Cl]₂)>

Next, 1.08 g of the pyrazine derivative Htppr obtained in the above step1 and 0.73 g of iridium chloride hydrate (IrCl₃.H₂O) (produced bySigma-Aldrich Corp.) were mixed in a mixed solution containing 30 mL of2-ethoxyethanol and 10 mL of water, and the mixture was refluxed in anitrogen atmosphere for 16 hours. A powder precipitated was filtered andwashed with ethanol, ether, and then hexane; thereby obtaining adinuclear complex [Ir(tppr)₂Cl]₂ (orange powder, yield of 97%). Asynthetic scheme of Step 2 is shown in the following (b-1).

<Step 3: Synthesis of(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: [Ir(tppr)₂(acac)])>

Further, 2.00 g of the dinuclear complex [Ir(tppr)₂Cl]₂ obtained in theabove step 2, 0.37 mL of acetylacetone and 1.26 g of sodium carbonatewere mixed in a solvent of 2-ethoxyethanol (40 mL), and the mixture wasrefluxed in a nitrogen atmosphere for 18 hours. After the reflux, themixture was filtered and the filtrate was left for one week. Then, acrystal precipitated was removed by filtration and a solvent of thefiltrate was distilled off. A residue obtained was recrystallized with amixed solvent of dichloromethane and ethanol. A powder obtained by therecrystallization washed with ethanol and then ether; thereby obtainingan organometallic complex [Ir(tppr)₂(acac)] of the present invention(red powder, yield of 16%). A synthetic scheme of Step 3 is shown in thefollowing (c-1).

An analysis result of the red powder obtained in Step 3 by nuclearmagnetic resonance spectrometry (¹H-NMR) is shown below. A ¹H-NMR chartis shown in FIGS. 10A and 10B. FIG. 10B shows an enlarged view of FIG.10A in the vertical axis direction. From FIGS. 10A and 10B, it was foundthat the organometallic complex [Ir(tppr)₂(acac)] of the presentinvention represented by the above structural formula (1) was obtainedin Synthetic Example 1.

¹H-NMR. δ (CDCl₃): 1.92 (s, 6H), 5.35 (s, 1H), 6.45-6.54 (m, 4H), 6.67(td, 2H), 6.91 (d, 2H), 7.41-7.57 (m, 12H), 7.81 (m, 4H), 8.08 (dd, 4H),8.98 (s, 2H).

A decomposition temperature T_(d) of the obtained organometallic complex[Ir(tppr)₂(acac)] of the present invention was measured byThermo-Gravimetric/Differential Thermal Analyzer (manufactured by SeikoInstrument Inc., TG/DTA 320 type), and the result was T_(d)=331° C. Itwas found that the obtained product showed favorable heat resistance.

Next, an absorption spectrum of [Ir(tppr)₂(acac)] was measured with theuse of an ultraviolet-visible light spectrophotometer (manufactured byJapan Spectroscopy Corporation, V550 type). The measurement wasconducted by using a degassed dichloromethane solution (0.10 mmol/L) ata room temperature. In addition, an emission spectrum of[Ir(tppr)₂(acac)] was measured with the use of a fluorescencespectrophotometer (manufactured by Hamamatsu Photonics Corporation,FS920). The measurement was conducted by using a degasseddichloromethane solution (0.35 mmol/L) at a room temperature. FIG. 11shows the measurement results. The horizontal axis indicates awavelength and the vertical axis indicates a molar absorptioncoefficient and emission intensity.

As shown in FIG. 11, the organometallic complex [Ir(tppr)₂(acac)] of thepresent invention has a peak of emission spectrum at 622 nm, andred-orange light was observed from the solution.

Further, it is observed that the organometallic complex[Ir(tppr)₂(acac)] of the present invention has several absorption peaksin a visible light region. This is an absorption unique to someorganometallic complexes, which is often observed in an ortho-metalatedcomplex or the like, and is considered to correspond to singlet MLCTtransition, triplet π-π* transition, triplet MLCT transition, or thelike. In particular, the absorption peak having the longest wavelengthspreads broadly in the visible light region, which would be owing totriplet MLCT transition. In other words, it was found that theorganometallic complex [Ir(tppr)₂(acac)] of the present invention was acompound capable of direct photo-excitation to a triplet excitated stateand intersystem crossing. Therefore, it can be considered that obtainedemission was light emission from the triplet excited state, in otherwords, phosphorescence.

<Synthetic Example 2>

In Synthetic Example 2, a synthetic method of 2,3,5-triphenylpyrazine(abbreviation: Htppr), which was synthesized in the above Step 1 ofSynthetic Example 1, different from the method of Synthetic Example 1,will be described.

First, 4.60 g of phenylglyoxal (produced by Tokyo Chemical IndustriesCo., Ltd.) and 7.28 g of meso-1,2-diphenylethylenediamine (produced bySigma-Aldrich Corp.) were mixed in a solvent of ethanol (200 mL), andthe mixture was refluxed in a nitrogen atmosphere for 6 hours. After thereflux, a solvent of this mixture was distilled off, and a residueobtained was recrystallized with ethanol. An ocher powder obtained bythe recrystallization was dissolved in dichloromethane, and thissolution was added with activated manganese dioxide excessively, mixedsufficiently, and then filtered. After a solvent of the filtrate wasdistilled off, a residue obtained was recrystallized with ethanol;thereby obtaining a pyrazine derivative Htppr (yellow powder, yield of37%). A synthetic scheme of Synthetic Example 2 is shown in thefollowing (a-1-2).

Example 2

Example 2 will describe a light emitting element of the presentinvention with reference to FIG. 12. Chemical formulae of materials usedin Examples 2 and 3 are shown below.

(Light Emitting Element 1)

First, indium tin oxide containing silicon oxide was formed over a glasssubstrate 2101 by sputtering as a first electrode 2102. The filmthickness of the first electrode 2102 was 110 nm and the area thereofwas 2 mm×2 mm.

Then, the substrate provided with the first electrode was fixed on asubstrate holder which was provided in a vacuum evaporation apparatus,in such a way that a surface provided with the first electrode faceddownward. After that, the air inside the vacuum evaporation apparatuswas evacuated to approximately 10⁻⁴ Pa. Then, a layer 2103 including acomposite material including an organic compound and an inorganiccompound was formed on the first electrode 2102 by co-evaporation of NPBand molybdenum (VI) oxide. The film thickness was 50 nm and the weightratio between NPB and molybdenum (VI) oxide was adjusted to be 4:1(=NPB:molybdenum oxide). It is to be noted that the co-evaporation is anevaporation method by which evaporation is carried out simultaneouslyfrom a plurality of evaporation sources in one process chamber.

Next, a hole transporting layer 2104 was formed on the layer includingthe composite material 2103 to have a thickness of 10 nm using4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB) byevaporation using resistance heating.

Further, a light emitting layer 2105 was formed on the hole transportinglayer 2104 to have a thickness of 30 nm by co-evaporation of2,3-bis{4-[N-(4-biphenylyl)-N-phenylamino]phenyl}quinoxaline(abbreviation: BPAPQ) and(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: Ir(tppr)₂(acac)) which is expressed by the structuralformula (1). Here, the weight ratio between BPAPQ and Ir(tppr)₂(acac)was adjusted to be 1:0.05 (=BPAPQ:Ir(tppr)₂(acac)).

After that, an electron transporting layer 2106 was formed on the lightemitting layer 2105 by depositingbis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation:BAlq) so as to have a thickness of 10 nm by evaporation using resistanceheating.

Further, an electron injecting layer 2107 was formed on the electrontransporting layer 2106 so as to have a thickness of 50 nm byco-evaporation of tris(8-quinolinolato)aluminum (abbreviation: Alq) andlithium. The weight ratio between Alq and lithium was adjusted to be1:0.01 (=Alq:lithium).

Finally, a second electrode 2108 was formed on the electron injectinglayer 2107 by depositing aluminum so as to have a thickness of 200 nm byevaporation using resistance heating. Thus, the light emitting element 1was formed.

Current density-luminance characteristics of the light emitting element1 are shown in FIG. 13. Voltage-luminance characteristics thereof areshown in FIG. 14. Luminance-current efficiency characteristics thereofare shown in FIG. 15. In addition, luminance-external quantum efficiencycharacteristics are shown in FIG. 16. Also, an emission spectrum uponapplying a current of 1 mA is shown in FIG. 17. From FIG. 17, it can befound that light emission of the light emitting element 1 is the lightemission of Ir(tppr)₂(acac). The CIE chromaticity coordinates of thelight emitting element 1 are (x, y)=(0.66, 0.34) when the luminance is1000 cd/m², and the light emitting element 1 emits red-color light.Further, as is seen from FIG. 16, the light emitting element 1 exhibitshigh external quantum efficiency. Therefore, the light emitting element1 has high light emission efficiency. From FIG. 15, it can be found thatthe light emitting element 1 has high luminous efficiency. Further, inFIG. 14, the voltage for obtaining a certain level of luminance is low,and this shows that the light emitting element 1 has small powerconsumption.

An initial luminance was set at 1000 cd/m², and the light emittingelement 1 of this example was driven under a condition of constantcurrent density. After a lapse of 100 hours, the light emitting element1 kept 97% of the initial luminance, which shows that the light emittingelement 1 hardly deteriorated.

Example 3

Example 3 will describe a light emitting element of the presentinvention with reference to FIG. 12.

(Light Emitting Element 2)

First, a film containing indium tin oxide containing silicon oxide wasformed over a glass substrate 2101 by sputtering as a first electrode2102. The film thickness of the first electrode was 110 nm and the areathereof was 2 mm×2 mm.

Then, the substrate provided with the first electrode was fixed on asubstrate holder which was provided in a vacuum evaporation apparatus,in such a way that a surface provided with the first electrode shouldface downward. After that, the air inside the vacuum evaporationapparatus was evacuated to approximately 10⁻⁴ Pa. Then, a layerincluding a composite material 2103 including an organic compound and aninorganic compound was formed on the first electrode 2102 byco-evaporation of NPB and molybdenum oxide (VI). The film thickness was50 nm and the weight ratio between NPB and molybdenum oxide (VI) wasadjusted to be 4:1 (=NPB:molybdenum oxide). Note that the co-evaporationis an evaporation method by which evaporation is carried outsimultaneously from a plurality of evaporation sources in one processchamber.

Next, a hole transporting layer 2104 was formed on the layer includingthe composite material 2103 so as to have a thickness of 10 nm using4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB) byevaporation using resistance heating.

Further, a light emitting layer 2105 was formed on the hole transportinglayer 2104 to have a thickness of 30 nm by co-evaporation ofbis[2-(2-hydroxyphenyl)benzoxazolato]zinc (abbreviation: Zn(PBO)₂) and(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: Ir(tppr)₂(acac)) which is expressed by the structuralformula (1). Here, the weight ratio between Zn(PBO)₂ and Ir(tppr)₂(acac)was adjusted to be 1:0.05 (=Zn(PBO)₂:Ir(tppr)₂(acac)).

After that, an electron transporting layer 2106 was formed on the lightemitting layer 2105 by depositingbis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation:BAlq) so as to have a thickness of 10 nm by evaporation using resistanceheating.

Further, an electron injecting layer 2107 was formed on the electrontransporting layer 2106 so as to have a thickness of 50 nm byco-evaporation of tris(8-quinolinolato)aluminum (abbreviation; Alq) andlithium. The weight ratio between Alq and lithium was adjusted to be1:0.01 (=Alq:lithium).

Finally, a second electrode 2108 was formed over the electron injectinglayer 2107 by depositing aluminum so as to have a thickness of 200 nm byevaporation using resistance heating. Thus, the light emitting element 2was formed.

Current density-luminance characteristics of the light emitting element2 are shown in FIG. 18. Voltage-luminance characteristics thereof areshown in FIG. 19. Luminance-current efficiency characteristics thereofare shown in FIG. 20. In addition, luminance-external quantum efficiencycharacteristics are shown in FIG. 21. Also, an emission spectrum uponapplying a current of 1 mA is shown in FIG. 22. From FIG. 22, it can befound that light emission of the light emitting element 2 is owing tothe light emission of Ir(tppr)₂(acac). The CIE chromaticity coordinatesof the light emitting element 2 are (x, y)=(0.67, 0.33) when theluminance is 1000 cd/m², and the light emitting element 2 emitsred-color light. Further, as is seen from FIG. 21, the light emittingelement 2 exhibits high external quantum efficiency. In particular, itcan be found that the light emitting element 2 has further higherexternal quantum efficiency than the light emitting element 1 formed inExample 1. The light emitting element 2 uses an organometallic complexof the present invention and a zinc complex for the light emittinglayer, which is considered as a cause of realizing higher externalquantum efficiency.

From FIG. 20, it is found that the light emitting element 2 has highluminous efficiency. Further, it can be found from FIG. 19 that thevoltage for obtaining a certain level of luminance is low. This showsthat the light emitting element 2 has small power consumption.

Example 4

<Synthetic Example 3 >

In Synthetic Example 3, a synthetic example of an organometallic complexof the present invention represented by structural formula (20) inEmbodiment Mode 1,(acetylacetonato)bis(2,3-diphenyl-5-p-tolylpyrazinato)iridium(III)(abbreviation: [Ir(dppr-MP)₂(acac)]), will be specifically described.

<Step 1: Synthesis of 2,3-diphenyl-5-p-tolylpyrazine (abbreviation:Hdppr-MP)>

First, 0.49 g of magnesium and 3 mL of THF were suspended in a nitrogenatmosphere, and a small amount of 1,2-dibromoethane was added thereto.Then, a mixed solution in which 3.42 g of 4-bromotoluene was dissolvedin 20 mL of THF was delivered by drops, and the mixture was stirred for3 hours under reflux and made into a Grignard reagent. Next, 4.22 g of2,3-diphenylpyrazine was dissolved in 20 mL of THF, and the Grignardreagent prepared before was delivered thereto by drops, and stirring wasconducted for 5 hours under reflux. Water was added to this mixture andan organic layer was extracted with chloroform. The organic layerobtained was dried with magnesium sulfate, and manganese dioxide wasadded into the dried solution. The mixture was shaken lightly and thenfiltered, and a solvent of this solution was distilled off. A residueobtained by distillation was dissolved in dichloromethane, and themixture was added with ethanol and then left, so that a yellow crystalwas precipitated. This crystal was filtered out and washed with ethanol;thereby obtaining an objective pyrazine derivative Hdppr-MP (yield of30%). A synthetic scheme of Step 1 is shown in the following (a-2).

<Step 2: Synthesis ofdi-μ-chloro-bis[bis(2,3-diphenyl-5-p-tolylpyrazinato)iridium(III)](abbreviation: [Ir(dppr-MP)₂Cl]₂)>

Next, 24 mL of 2-ethoxyethanol, 8 mL of water, 0.64 g of the pyrazinederivative Hdppr-MP obtained in the above Step 1, and 0.30 g of iridiumchloride hydrate (IrCl₃.H₂O) (produced by Sigma-Aldrich Corp.) were putin an eggplant-type flask with a reflux pipe, and the inside air of theflask was substituted by argon. Then, a reaction was carried out byirradiation with microwave (2.45 GHz, 150 W) for 1 hour. An orangepowder precipitated from the reacted solution was filtered and washedwith ethanol; thereby obtaining a dinuclear complex [Ir(dppr-MP)₂Cl₂](yield of 58%). The irradiation of microwave was conducted using amicrowave synthesis system (Discovery, manufactured by CEM Corporation).A synthetic scheme of Step 2 is shown in the following (b-2).

<Step 3: Synthesis of(acetylacetonato)bis(2,3-diphenyl-5-p-tolylpyrazinato)iridium(III)(abbreviation: [Ir(dppr-MP)₂(acac)]>

Next, 20 mL of 2-ethoxyethanol, 0.50 g of the dinuclear complex[Ir(dppr-MP)₂Cl]₂ obtained in the above Step 2, 0.09 mL ofacetylacetone, and 0.31 g of sodium carbonate were put in aneggplant-type flask with a reflux pipe, and the inside air of the flaskwas substituted by argon. Then, a reaction was carried out byirradiation with microwave (2.45 GHz, 150 W) for 30 minutes. The reactedsolution was filtered, and a filtrate obtained was condensed and dried.A residue obtained was recrystallized with ethanol, and a red powderobtained washed with ethanol and then ether; thereby obtaining anorganometallic complex of the present invention [Ir(dppr-MP)₂(acac)](yield of 96%). A synthetic scheme of Step 3 is shown in the following(c-2).

An analysis result of the red powder obtained in Step 3 by nuclearmagnetic resonance spectrometry (¹H-NMR) is shown below. A ¹H-NMR chartis shown in FIGS. 24A and 24B. From FIGS. 24A and 24B, it was found thatthe organometallic complex [Ir(dppr-MP)₂(acac)] of the present inventionrepresented by the above structural formula (20) was obtained inSynthetic Example 3.

¹H-NMR. δ (CDCl₃): 1.91 (s, 6H), 2.44 (s, 6H), 5.33 (s, 1H), 6.47 (m,4H), 6.66 (t, 2H), 6.89 (d, 2H), 7.33 (m, 5H), 7.54 (m, 7H), 7.80 (m,4H), 7.79 (d, 4H), 8.94 (s, 2H).

A decomposition temperature of the obtained organometallic complex[Ir(dppr-MP)₂(acac)] of the present invention was measured using ahigh-vacuum differential type differential thermalanalyzer/thermogravimetry-differential thermal analyzer (manufactured byBruker AXS K.K., TG-DTA2410SA). The rising temperature rate was set at10° C./min. When the temperature was raised at a normal pressure, 5% ofgravity reduction was seen at a temperature of 338° C., and it was foundthat the organometallic complex exhibited excellent heat resistance.

Next, an absorption spectrum of [Ir(dppr-MP)₂(acac)] was measured withthe use of an ultraviolet-visible light spectrophotometer (manufacturedby Japan Spectroscopy Corporation, V550 type). The measurement wasconducted by using a dichloromethane solution (0.10 mmol/L) at a roomtemperature. In addition, an emission spectrum of [Ir(dppr-MP)₂(acac)]was measured with the use of a fluorescence spectrophotometer(manufactured by Hamamatsu Photonics Corporation, FS920). Themeasurement was conducted by using a degassed dichloromethane solution(0.35 mmol/L) at a room temperature. FIG. 25 shows the measurementresults. The horizontal axis indicates a wavelength and the verticalaxis indicates a molar absorption coefficient and emission intensity.

As shown in FIG. 25, the organometallic complex [Ir(dppr-MP)₂(acac)] ofthe present invention has a peak of emission spectrum at 620 nm, and redlight was observed from the solution.

Example 5

<Synthetic Example 4 >

In Synthetic Example 4, a synthetic example of an organometallic complexof the present invention represented by structural formula (27) inEmbodiment Mode 1,(acetylacetonato)bis(5-phenyl-2,3-di-p-tolylpyrazinato)iridium(III)(abbreviation: [Ir(Mdppr-P)₂(acac)]), will be specifically described.

<Step 1: Synthesis of 2,3-di-p-tolylpyrazine>

First, 25.52 g of 4,4′-dimethylbenzyl and 6.44 g of anhydrousethylenediamine were dissolved in a solvent of dehydrated ethanol (300mL) in a nitrogen atmosphere and reacted for 12.5 hours by refluxing.34.71 g of iron oxide (III) was added into this reacted solution, and areaction was carried out by slowly stirring the solution while beingheated at 70° C. or lower for 2.5 hours. Water was added into thismixture and an organic layer was extracted with dichloromethane. Theorganic layer obtained was dried with magnesium sulfate. After thedrying, filtration was conducted and a solvent of this solution wasdistilled off. A residue obtained by the distillation was purified bysilica gel column chromatography which uses dichloromethane as adeveloping solvent; thereby obtaining an intermediate,2,3-di-p-tolylpyrazine (orange powder, yield of 31%).

<Step 2: Synthesis of 5-phenyl-2,3-di-p-tolylpyrazine (abbreviation:HMdppr-P)>

Next, in a nitrogen atmosphere, 6.48 mL of a dibutyl ether solutioncontaining phenyl lithium (produced by Wako Pure Chemical Industries,Ltd., 2.1 mol/L) and 80 mL of diethylether were mixed. While the mixedsolution was being cooled with ice, 3.22 g of 2,3-di-p-tolylpyrazinewhich was an intermediate obtained in the above Step 1 was added theretoand stirred at a room temperature for 24 hours. Water was added intothis mixture, and an organic layer was extracted with dichloromethane.The organic layer obtained washed with water and dried with magnesiumsulfate. The solution after drying was added with activated manganesedioxide excessively and filtration was conducted. After a solvent ofthis solution was distilled off, a residue obtained by the distillationwas purified by silica gel column chromatography which usesdichloromethane as a developing solvent; thereby obtaining an objectivepyrazine derivative HMdppr-P (orange powder, yield of 22%). A syntheticscheme of Step 1 and Step 2 is shown in the following (a-3).

<Step 3: Synthesis ofdi-μ-chloro-bis[bis(5-phenyl-2,3-di-p-tolylpyrazinato)iridium(III)](abbreviation: [Ir(Mdppr-P)₂Cl]₂)>

18 mL of 2-ethoxyethanol, 6 mL of water, 0.82 g of the pyrazinederivative HMdppr-P obtained in the above Step 2, and 0.36 g of iridiumchloride hydrate (IrCl₃.H₂O) (produced by Sigma-Aldrich Corp.) were putin an eggplant-type flask with a reflux pipe, and the inside air of theflask was substituted by argon. Then, a reaction was carried out byirradiation with microwave (2.45 GHz, 200 W) for 1 hour. An orangepowder precipitated from the reacted solution was filtered and washedwith ethanol; thereby obtaining a dinuclear complex [Ir(Mdppr-P)₂Cl]₂(yield of 82%). The irradiation of microwave was conducted using amicrowave synthesis system (Discovery, manufactured by CEM Corporation).A synthetic scheme of Step 3 is shown in the following (b-3).

<Step 4: Synthesis of(acetylacetonato)bis(5-phenyl-2,3-di-p-tolylpyrazinato)iridium(III)(abbreviation: [Ir(Mdppr-P)₂(acac)]>

Next, 20 mL of 2-ethoxyethanol, 0.44 g of the dinuclear complex[Ir(Mdppr-P)₂Cl]₂ obtained in the above Step 3, 0.08 mL ofacetylacetone, and 0.25 g of sodium carbonate were put in aneggplant-type flask with a reflux pipe, and the inside air of the flaskwas substituted by argon. Then, a reaction was carried out byirradiation with microwave (2.45 GHz, 200 W) for 30 minutes. The reactedsolution was filtered, and then a filtrate obtained was condensed anddried. A residue obtained was recrystallized with ethanol, and a redpowder obtained washed with ethanol and then ether; thereby obtaining anorganometallic complex of the present invention, [Ir(Mdppr-P)₂(acac)](yield of 31%). A synthetic scheme of Step 4 is shown in the following(c-3).

An analysis result of the red powder obtained in Step 4 by nuclearmagnetic resonance spectrometry (¹H-NMR) is shown below. A ¹H-NMR chartis shown in FIGS. 26A and 26B. From FIGS. 26A and 26B, it was found thatthe organometallic complex [Ir(Mdppr-P)₂(acac)] of the present inventionrepresented by the above structural formula (27) was obtained inSynthetic Example 4.

¹H-NMR. δ (CDCl₃): 1.91 (s, 6H), 2.02 (s, 6H), 2.48 (s, 6H), 5.33 (s,1H), 6.28 (s, 2H), 6.36 (d, 2H), 6.88 (d, 2H), 7.33 (m, 4H), 7.51 (m,6H), 7.72 (d, 4H), 8.08 (d, 4H), 8.91 (s, 2H).

A decomposition temperature of the obtained organometallic complex[Ir(Mdppr-P)₂(acac)] of the present invention was measured using ahigh-vacuum differential type differential thermalanalyzer/thermogravimetry-differential thermal analyzer (manufactured byBruker AXS K.K., TG-DTA2410SA). The rising temperature rate was set at10° C./min. When the temperature was raised at a normal pressure, 5% ofgravity reduction was seen at a temperature of 342° C., and it was foundthat the organometallic complex exhibited excellent heat resistance.

Next, an absorption spectrum of [Ir(Mdppr-P)₂(acac)] was measured withthe use of an ultraviolet-visible light spectrophotometer (manufacturedby Japan Spectroscopy Corporation, V550 type). The measurement wasconducted by using a dichloromethane solution (0.096 mmol/L) at a roomtemperature. In addition, an emission spectrum of [Ir(Mdppr-P)₂(acac)]was measured with the use of a fluorescence spectrophotometer(manufactured by Hamamatsu Photonics Corporation, FS920). Themeasurement was conducted by using a degassed dichloromethane solution(0.34 mmol/L) at a room temperature. FIG. 27 shows the measurementresults. The horizontal axis indicates a wavelength and the verticalaxis indicates a molar absorption coefficient and emission intensity.

As shown in FIG. 27, the organometallic complex [Ir(Mdppr-P)₂(acac)] ofthe present invention has a peak of emission spectrum at 620 nm, and redlight was observed from the solution.

<Example 6>

<Synthetic Example 5>

In Synthetic Example 5, a synthetic example of an organometallic complexof the present invention represented by structural formula (3) inEmbodiment Mode 1, bis(2,3,5-tolylpyrazinato)(picolinato)iridium(III)(abbreviation: [Ir(tppr)₂(pic)]), will be specifically described.

<Synthesis of bis(2,3,5-triphenylpyrazinato)(picolinato)iridium(III)(abbreviation; [Ir(tppr)₂(pic)]>

25 mL of dichloromethane, 0.84 g of the dinuclear complex [Ir(tppr)₂Cl]₂obtained in Step 2 of Synthetic Example 1, and 0.49 g of picolinic acidwere put in an eggplant-type flask with a reflux pipe, and the insideair of the flask was substituted by argon. Then, a reaction was carriedout by irradiation with microwave (2.45 GHz, 100 W) for 30 minutes. Thereacted solution was filtered, and a filtrate obtained was condensed anddried. A residue obtained was recrystallized with a mixed solvent ofmethanol and dichloromethane; thereby obtaining an organometalliccomplex of the present invention, [Ir(tppr)₂(pic)] (yield of 84%,red-orange powder). The irradiation of microwave was conducted using amicrowave synthesis system (Discovery, manufactured by CEM Corporation).A synthetic scheme of this complex is shown in the following (c-4).

An analysis result of the red-orange powder obtained by the above stepby nuclear magnetic resonance spectrometry (¹H-NMR) is shown below. A¹H-NMR chart is shown in FIGS. 28A and 28B. From FIGS. 28A and 28B, itwas found that the organometallic complex [Ir(tppr)₂(pic)] of thepresent invention represented by the above structural formula (3) wasobtained in Synthetic Example 5.

¹H-NMR. δ (CDCl₃): 6.42 (d, 1H), 6.58 (m, 3H), 6.77 (m, 2H), 6.93 (m,2H), 7.39 (m, 3H), 7.45-7.56 (m, 8H), 7.67 (m, 4H), 7.77 (m, 4H), 8.09(m, 3H), 8.48 (d, 1H), 8.28 (s, 1H).

A decomposition temperature of the obtained organometallic complex[Ir(tppr)₂(pic)] of the present invention was measured using ahigh-vacuum differential type differential thermalanalyzer/thermogravimetry-differential thermal analyzer (manufactured byBruker AXS K.K., TG-DTA2410SA). The rising temperature rate was set at10° C./min. When the temperature was raised at a normal pressure, 5% ofgravity reduction was seen at a temperature of 368° C., and it was foundthat the organometallic complex exhibited excellent heat resistance.

Next, an absorption spectrum of [Ir(tppr)₂(pic)] was measured with theuse of an ultraviolet-visible light spectrophotometer (manufactured byJapan Spectroscopy Corporation, V550 type). The measurement wasconducted by using a dichloromethane solution (0.10 mmol/L) at a roomtemperature. In addition, an emission spectrum of [Ir(tppr)₂(pic)] wasmeasured with the use of a fluorescence spectrophotometer (manufacturedby Hamamatsu Photonics Corporation, FS920). The measurement wasconducted by using a degassed dichloromethane solution (0.35 mmol/L) ata room temperature. FIG. 29 shows the measurement results. Thehorizontal axis indicates a wavelength and the vertical axis indicates amolar absorption coefficient and emission intensity.

As shown in FIG. 29, the organometallic complex [Ir(tppr)₂(pic)] of thepresent invention has a peak of emission spectrum at 606 nm, and orangelight was observed from the solution.

Example 7

<Synthetic Example 6>

In Synthetic Example 6, a synthetic example of an organometallic complexof the present invention represented by structural formula (34) inEmbodiment Mode 1,(acethylacetonato)bis(3-methyl-2,5-diphenylpyrazinato)iridium(III)(abbreviation: [Ir(mppr-P)₂(acac)]), will be specifically described.

<Step 1: Synthesis of 3-methyl-2,5-diphenylpyrazine (abbreviation:Hmppr-P)>

In a nitrogen atmosphere, 10 mL of a dibutyl ether solution containingphenyl lithium (produced by Wako Pure Chemical Industries, Ltd., 2.1mol/L) and 120 mL of diethylether were mixed. While the mixed solutionwas being cooled with ice, 2.87 g of 2-methyl-3-phenylpyrazine was addedthereto and stirred at a room temperature for 24 hours. Water was addedinto this mixture, and an organic layer was extracted with ethylacetate. The organic layer obtained was dried with magnesium sulfate.The solution after drying was added with activated manganese dioxideexcessively and filtration was conducted. A solvent of the obtainedfiltrate was distilled off, so that a residue was obtained. This residuewas purified by silica gel column chromatography which usesdichloromethane as a developing solvent; thereby obtaining an objectivepyrazine derivative Hmppr-P (orange oily substance, yield of 12%). Asynthetic scheme of Step 1 is shown in the following (a-5).

<Step 2: Synthesis ofdi-μ-chloro-bis[bis(3-methyl-2,5-diphenylpyrazinato)iridium(III)](abbreviation: [Ir(mppr-P)₂Cl₂]>

Next, 21 mL of 2-ethoxyethanol, 7 mL of water, 0.49 g of the pyrazinederivative Hmppr-P obtained in the above Step 1, and 0.30 g of iridiumchloride hydrate (IrCl₃.H₂O) (produced by Sigma-Aldrich Corp.) were putin an eggplant-type flask with a reflux pipe, and the inside air of theflask was substituted by argon. Then, a reaction was carried out byirradiation with microwave (2.45 GHz, 150 W) for 30 minutes. An orangepowder precipitated from the reacted solution was filtered and washedwith ethanol; thereby obtaining a dinuclear complex [Ir(mppr-P)₂Cl]₂(yield of 10%). The irradiation of microwave was conducted using amicrowave synthesis system (Discovery, manufactured by CEM Corporation).A synthetic scheme of Step 2 is shown in the following (b-5).

<Step 3: synthesis of(acetylacetonato)bis(3-methyl-2,5-diphenylpyrazinato)iridium(III)(abbreviation: [Ir(mppr-P)₂(acac)])>

Next, 10 mL of 2-ethoxyethanol, 0.14 g of the dinuclear complex[Ir(mppr-P)₂Cl]2 obtained in the above Step 2, 0.03 mL of acetylacetone,and 0.10 g of sodium carbonate were put in an eggplant-type flask with areflux pipe, and the inside air of the flask was substituted by argon.Then, a reaction was carried out by irradiation with microwave (2.45GHz, 100 W) for 30 minutes. A red-orange powder precipitated from thereacted solution was filtered, and washed with water, ethanol, and thenether; thereby obtaining an organometallic complex of the presentinvention, [Ir(mppr-P)₂(acac)] (yield of 77%). A synthetic scheme ofStep 3 is shown in the following (c-5).

An analysis result of the red-orange powder obtained by the above stepby nuclear magnetic resonance spectrometry (¹H-NMR) is shown below. A¹H-NMR chart is shown in FIGS. 30A and 30B. From FIGS. 30A and 30B, itwas found that the organometallic complex [Ir(mppr-P)₂(acac)] of thepresent invention represented by the above structural formula (34) wasobtained in Synthetic Example 6.

¹H-NMR. δ (CDCl₃): 1.85 (s, 6H), 3.17 (s, 6H), 5.29 (s, 1H), 6.35 (d,2H), 6.72 (t, 2H), 6.91 (t, 2H), 7.55 (m, 6H), 7.95 (d, 2H), 8.06 (d,4H), 8.93 (s, 2H).

Next, an absorption spectrum of [Ir(mppr-P)₂(acac)] was measured withthe use of an ultraviolet-visible light spectrophotometer (manufacturedby Japan Spectroscopy Corporation, V550 type). The measurement wasconducted by using a dichloromethane solution (0.12 mmol/L) at a roomtemperature. In addition, an emission spectrum of [Ir(mppr-P)₂(acac)]was measured with the use of a fluorescence spectrophotometer(manufactured by Hamamatsu Photonics Corporation, FS920). Themeasurement was conducted by using a degassed dichloromethane solution(0.41 mmol/L) at a room temperature. FIG. 31 shows the measurementresults. The horizontal axis indicates a wavelength and the verticalaxis indicates a molar absorption coefficient and emission intensity.

As shown in FIG. 31, the organometallic complex [Ir(mppr-P)₂(acac)] ofthe present invention has a peak of emission spectrum at 607 nm, andorange light was observed from the solution.

Example 8

Example 8 will describe a light emitting element of the presentinvention with reference to FIG. 12. A chemical formula of a material tobe used in this example is shown below.

(Light Emitting Element 3)

First, indium tin oxide containing silicon oxide was formed over a glasssubstrate 2101 by sputtering as a first electrode 2102. The filmthickness of the first electrode 2102 was 110 nm and the area thereofwas 2 mm×2 mm.

Then, the substrate provided with the first electrode was fixed on asubstrate holder which was provided in a vacuum evaporation apparatus,in such a way that a surface provided with the first electrode faceddownward. After that, the air inside the vacuum evaporation apparatuswas evacuated to approximately 10⁻⁴ Pa. Then, a layer including acomposite material 2103 including an organic compound and an inorganiccompound was formed on the first electrode 2102 by co-evaporation of NPBand molybdenum oxide (VI). The film thickness was 50 nm and the weightratio between NPB and molybdenum oxide (VI) was adjusted to be 4:1(=NPB:molybdenum oxide). Note that the co-evaporation is an evaporationmethod by which evaporation is carried out simultaneously from aplurality of evaporation sources in one process chamber.

Next, a hole transporting layer 2104 was formed on the layer includingthe composite material 2103 to have a thickness of 10 nm using4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (abbreviation: NPB) byevaporation using resistance heating.

Further, a light emitting layer 2105 was formed on the hole transportinglayer 2104 to have a thickness of 30 nm by co-evaporation of4-(9H-carbazole-9-yl)-4′-(5-phenyl-1,3,4-oxadiazole-2-yl)triphenylamine)(abbreviation: YGAO11) and(acetylacetonato)bis(2,3,5-triphenylpyrazinato)iridium(III)(abbreviation: Ir(tppr)₂(acac)) which is expressed by the structuralformula (1). Here, the weight ratio between YGAO11 and Ir(tppr)₂(acac)was adjusted to be 1:0.06 (=YGAO11:Ir(tppr)₂(acac)).

After that, an electron transporting layer 2106 was formed on the lightemitting layer 2105 by depositingbis(2-methyl-8-quinolinolato)(4-phenylphenolato)aluminum (abbreviation:BAlq) so as to have a thickness of 10 nm by evaporation using resistanceheating.

Further, an electron injecting layer 2107 was formed on the electrontransporting layer 2106 so as to have a thickness of 50 nm byco-evaporation of tris(8-quinolinolato)aluminum (abbreviation: Alq) andlithium. The weight ratio between Alq and lithium was adjusted to be1:0.01 (=Alq:lithium).

Finally, a second electrode 2108 was formed on the electron injectinglayer 2107 by depositing aluminum so as to have a thickness of 200 nm byevaporation using resistance heating. Thus, the light emitting element 3was formed.

Current density-luminance characteristics of the light emitting element3 are shown in FIG. 32. Voltage-luminance characteristics thereof areshown in FIG. 33. Luminance-current efficiency characteristics thereofare shown in FIG. 34. In addition, luminance-external quantum efficiencycharacteristics are shown in FIG. 35. Also, an emission spectrum uponapplying a current of 1 mA is shown in FIG. 36. From FIG. 36, it can befound that light emission of the light emitting element 3 is the lightemission of Ir(tppr)₂(acac). The CIE chromaticity coordinates of thelight emitting element 3 are (x, y)=(0.67, 0.34) when the luminance is1000 cd/m², and the light emitting element 3 emits red-color light.Further, as is seen from FIG. 35, the light emitting element 3 exhibitshigh external quantum efficiency. Particularly, it can be found that thelight emitting element 3 has further higher external quantum efficiencythan the light emitting element 1 formed in Example 1. The lightemitting element 3 uses an organometallic complex of the presentinvention and a zinc complex for the light emitting layer, which isconsidered as a cause of realizing higher external quantum efficiency.

From FIG. 34, it is found that the light emitting element 3 has highluminous efficiency. Further, it is found from FIG. 33 that the voltagefor obtaining a certain level of luminance is low. This shows that thelight emitting element 3 has small power consumption.

Example 9

Example 9 will describe the materials used in other examples.

<Synthetic Example of Bpapq>

In this synthetic example, a synthetic method of2,3-bis{4-[N-(4-biphenylyl)-N-phenylamino]phenyl} quinoxaline(abbreviation: BPAPQ) which is represented by the following structuralformula (201) will be described.

[Step 1]

A synthetic method of 2,3-bis(4-bromophenyl)quinoxaline will bedescribed. A synthetic scheme of 2,3-bis(4-bromophenyl)quinoxaline willbe shown in (D-1).

In a nitrogen atmosphere, a chloroform solution (200 mL) containing 30.0g (81.5 mmol) of 4,4′-dibromobenzyl and 9.00 g (83.2 mmol) ofo-phenylenediamine was refluxed at 80° C. for three hours. The reactedsolution washed with water after being cooled to a room temperature. Anaqueous layer was extracted with chloroform and the solution obtained byextraction washed with saturated saline together with the organic layer.After the organic layer was dried with magnesium sulfate, the mixturewas filtered and the filtrate was condensed. Accordingly, 33 g (yield:92%) of objective 2,3-bis(4-bromophenyl)quinoxaline was obtained as awhite solid.

[Step 2]

A synthetic method of N-(4-biphenylyl)-N-phenylamine will be described.A synthetic scheme of N-(4-biphenylyl)-N-phenylamine is shown in (D-2).

In a nitrogen atmosphere, a xylene suspension (150 mL) containing 20.0 g(85.8 mmol) of 4-bromobiphenyl, 16.0 g (172 mmol) of aniline, 0.19 g(0.858 mmol) of palladium acetate, and 23.7 g (172 mmol) of potassiumcarbonate, to which 5.2 g (2.5 mmol) of tri-tert-butylphosphine (10%hexane solution) was added, was refluxed at 120° C. for ten hours. Aftercompletion of reaction, the reaction mixture washed with water and anaqueous layer was extracted with toluene. The toluene layer was washedwith saturated saline together with an organic layer, and drying withmagnesium sulfate was conducted. Then, the mixture was subjected tofiltration and the filtrate was condensed. A residue obtained waspurified by silica gel column chromatography (developing solution:toluene). The obtained solution was condensed to obtain 13.5 g (yield:64%) of N-phenyl-N-(4-phenyl)-phenylamine as a white solid.

[Step 3]

A synthetic method of 2,3-bis{4-[N-(4-biphenylyl)-N-phenylamino]phenyl}quinoxaline (hereinafter referred to as BPAPQ) is described. A syntheticscheme of BPAPQ is shown in (D-3).

In a nitrogen atmosphere, a toluene suspension (80 mL) containing 5.0 g(11.4 mmol) of 2,3-bis(4-bromophenyl)quinoxaline, 6.1 g (25.0 mmol) ofN-(4-biphenylyl)-N-phenylamine, 0.33 g (0.58 mmol) ofbis(dibenzylidineacetone)palladium, and 5.5 g (56.8 mmol) of tert-butoxysodium, to which 1.2 g (0.58 mmol) of tri-tert-butylphosphine (10%hexane solution) was added, was heated at 80° C. for seven hours. Aftercompletion of reaction, the reaction mixture was cooled to a roomtemperature and the precipitate was collected by filtration. Theobtained filtrate was dissolved in toluene, the solution was subjectedto filtration through celite, Florisil, and alumina, and the filtratewas condensed. The obtained residue was recrystallized withchloroform-hexane to obtain 8.1 g (yield: 78%) of BPAPQ as a yellowsolid.

An analysis result of BPAPQ by a proton nuclear magnetic resonancespectroscopy (¹H NMR) is as follows. ¹H NMR (300 MHz, CDCl₃);δ=8.16-8.13 (m, 2H), 7.75-7.72 (m, 2H), 7.58-7.04 (m, 36H). FIG. 23Ashows an NMR chart of BPAPQ, and FIG. 23B shows an enlarged NMR chart ofa part of 6 to 9 ppm.

SYNTHETIC EXAMPLE OF YGAO11

In this synthetic example, a synthetic example of4-(9H-carbazole-9-yl)-4′-(5-phenyl-1,3,4-oxadiazole-2-yl)triphenylamine)(abbreviation: YGAO11), which is an oxadiazole derivative of the presentinvention represented by the following structural formula (202) will bespecifically described.

<Step 1: Synthesis of 2-(4-bromophenyl)-5-phenyl-1,3,4-oxadiazole(abbreviation: O11Br)>

In Step 1, O11Br was synthesized in accordance with (i) to (iii) shownbelow.

(i) Synthesis of 4-bromobenzohydrazide

First, 3.0 g (13.9 mmol) of methyl-4-bromobenzoate was put in a 100-mLthree-neck flask, 10 mL of ethanol was added therein, and the mixturewas stirred. Thereafter, 4.0 mL of hydrazine monohydrate was addedtherein, and the mixture was heated and stirred at 78° C. for 5 hours. Asolid obtained washed with water and collected by suction filtration;thus, 2.0 g of a white solid of objective 4-bromobenzohydrazide wasobtained (yield: 67%).

(ii) Synthesis of 1-benzoyl-2-(4-bromobenzoyl)hydrazine

Then, 2.0 g (13.9 mmol) of 4-bromobenzohydrazide obtained in (i) abovewas put in a 300-mL three-neck flask, 7 mL of N-methyl-2-pyrrolidone(abbreviation: NMP) was added therein, and the mixture was stirred.Thereafter, a mixture of 2.5 mL of N-methyl-2-pyrrolidone and 2.5 mL(21.5 mmol) of benzoyl chloride was dropped through a 50-mL droppingfunnel, and the mixture was stirred at 80° C. for 3 hours. A solidobtained washed with water and a sodium carbonate aqueous solution inthis order and collected by suction filtration. Then, the solid wasrecrystallized with acetone; thus, 3.6 g of a white solid of objective1-benzoyl-2-(4-bromobenzoyl)hydrazine was obtained (yield: 80%).

(iii) synthesis of o11Br

Further, 15 g (47 mmol) of 1-benzoyl-2-(4-bromobenzoyl)hydrazineobtained by the method shown in (ii) above was put in a 200-mLthree-neck flask, 100 mL of phosphoryl chloride was added therein, andthe mixture was heated and stirred at 100° C. for 5 hours. After thereaction, a solid obtained by completely distilling off phosphorylchloride washed with water and a sodium carbonate aqueous solution inthis order and collected by suction filtration. Then, the solid wasrecrystallized with methanol; thus, 13 g of a white solid of O11Br thatwas an object of Step 1 was obtained (yield: 89%). A synthetic scheme ofStep 1 described above is shown in the following scheme (E-1).

<Step 2: Synthesis of 4-(9H-carbazole-9-yl)diphenylamine (abbreviation:YGA)>

In Step 2, YGA was synthesized according to (i) and (ii) shown below.

(i) Synthesis of 9-(4-bromophenyl)carbazole

First, 56 g (240 mmol) of p-dibromobenzene, 31 g (180 mmol) ofcarbazole, 4.6 g (24 mmol) of copper iodide, 66 g (480 mmol) ofpotassium carbonate, and 2.1 g (8 mmol) of 18-crown-6-ether were put ina 300-mL three-neck flask, and nitrogen was substituted for air in theflask. Then, 8 mL of N,N′-dimethylpropyleneurea (abbreviation: DMPU) wasadded therein, and the mixture was stirred at 180° C. for 6 hours. Afterthe reaction mixture was cooled to room temperature, a precipitate wasremoved by suction filtration. The filtrate washed with dilutehydrochloric acid, a saturated sodium hydrogen carbonate aqueoussolution, and a saturated saline solution in this order and dried withmagnesium sulfate. After being dried, the solution was filterednaturally and condensed, and an obtained oily substance was purified bysilica gel column chromatography (hexane:ethyl acetate=9:1) andrecrystallized with chloroform and hexane; thus, 21 g of an objectivelight brown plate-shaped crystal of 9-(4-bromophenyl)carbazole wasobtained (yield: 35%).

(ii) Synthesis of YGA

Next, 5.4 g (17 mmol) of 9-(4-bromophenyl)carbazole that was obtained in(i) above, 1.8 mL (20 mmol) of aniline, 0.1 g (0.2 mmol) ofbis(dibenzylideneacetone)palladium(0), and 3.9 g (40 mmol) ofsodium-tert-butoxide were put in a 200-mL three-neck flask, and nitrogenwas substituted for air in the flask. Then, 0.1 mL of a 10% hexanesolution of tri(tert-butyl)phosphine and 50 mL of toluene were addedtherein, and the mixture was stirred at 80° C. for 6 hours. After thereaction mixture was filtered through Florisil, Celite, and alumina, thefiltrate was washed with water and a saturated saline solution and driedwith magnesium sulfate. After being dried, the solution was filterednaturally and condensed, and an obtained oily substance was purified bysilica gel column chromatography (hexane:ethyl acetate=9:1); thus, 4.1 gof YGA that was an object of Step 2 was obtained (yield: 73%). Thesynthetic scheme of Step 2 as described above is shown in the followingscheme (E-2).

<Step 3: Synthesis of4-(9H-carbazole-9-yl)-4′-(5-phenyl-1,3,4-oxadiazole-2-yl)triphenylamine)(abbreviation: YGAO11)>

3.0 g (10.0 mmol) of O11Br obtained in Step 1, 3.4 g (10.0 mmol) of YGAobtained in Step 2, and 1.9 g (19.9 mmol) of sodium-tert-butoxide wereput in a 100-mL three-neck flask, and nitrogen was substituted for airin the flask. Then, 45 mL of toluene, 0.3 mL of a 10% hexane solution oftri(tert-butyl)phosphine, and 0.3 g (0.6 mmol) ofbis(dibenzylideneacetone)palladium(0) were added therein, and themixture was heated and stirred at 120° C. for 5 hours. After thereaction, the mixture was filtered through Celite, and the filtratewashed with water and dried with magnesium sulfate. After being dried,the solution was filtered, and the filtrate was condensed. A solidobtained was dissolved in toluene and purified by silica gel columnchromatography. Purification by column chromatography was performed byusing toluene as a developing solvent and then using a mixed solvent oftoluene:ethyl acetate=1:1 as a developing solvent. The purified solidwas recrystallized with chloroform and hexane; thus, 4.7 g of a lightyellow solid YGAO11 that was an object of Synthesis Example 1 wasobtained (yield: 85%). The synthetic scheme of Step 3 as described aboveis shown in the following scheme (E-3).

An analysis result of the obtained YGAO11 by nuclear magnetic resonancespectroscopy (¹H-NMR) is shown below. FIG. 37A shows an ¹H-NMR chart andFIG. 37B shows an enlarged chart thereof. Accordingly, it was found thatthe YGAO11 represented by the above structural formula (202) wasobtained in Synthesis Example 1.

¹H-NMR (CDCl₃, 300 MHz): δ=7.14-7.53 (m, 19H), δ=8.03 (d, J=8.7, 2H),δ=8.11-8.15 (m, 4H)

In addition, sublimation purification of the obtained YGAO11 wasperformed by a train sublimation method. Under a reduced pressure of 7Pa, sublimation purification was performed at 265° C. for 12 hours,setting the flow rate of argon to be 3 mL/min. When sublimationpurification was performed on 4.5 g of YGAO11, the yield was 3.4 g and76%.

Further, the optimal molecular structure of YGAO11 in the ground statewas calculated using the B3LYP/6-311 (d, p) of the density functionaltheory (DFT). The accuracy of calculation of the DFT is higher than thatof a Hartree-Fock (HF) method which does not consider electroncorrelation. In addition, calculation costs for the DFT are lower thanthat of a method of perturbation (MP) which has the same level ofaccuracy of calculation as that of the DFT. Therefore, the DFT wasemployed for this calculation. The calculation was performed using ahigh performance computer (HPC) (Altix3700 DX, by SGI Japan, Ltd.). Whensinglet excitation energy (energy gap) of YGAO11 was calculated usingthe B3LYP/6-311 (d, p) of a time-dependent density functional theory(TDDFT) in the molecular structure optimized by the DFT, the singletexcitation energy was 3.18 eV. In addition, when triplet excitationenergy of YGAO11 was calculated, it was 2.53 eV. According to the aboveresults, it is understood that the oxadiazole derivative of the presentinvention is a substance having high excitation energy, in particular, asubstance having high triplet excitation energy.

Example 10

<Synthetic Example 7>

In the organometallic complex represented by the general formula (G12)in the embodiment mode, Synthetic Example 7 will specifically describe asynthetic example of an organometallic complex of the present inventionrepresented by structural formula (45), in which each of R⁴ and R⁹ is amethyl group, each of R³, R⁵ to R⁸, and R¹⁰ to R¹¹ is hydrogen, A_(r) ¹is a 3-fluorophenyl group, and L is a ligand represented by structuralformula (L1), that is(acethylacetonato)bis[5-(3-fluorophenyl)-2,3-di-p-tolylpyrazinato]iridium(III)(abbreviation: [Ir(Mdppr-3FP)₂(acac)]).

<Step 1: Synthesis of 5-(3-fluorophenyl)-2,3-di-p-tolylpyrazine(abbreviation: HMdppr-3FP)>

In a nitrogen atmosphere, 11 mL of a hexane solution (1.58 mol/L) ofn-butyllithium was dropped into a mixed solution of 2.86 g of3-bromofluorobenzene and 16 mL of tetrahydrofuran at −78° C., and thesolution was stirred for 2 hours, keeping the temperature at −78° C. Thesolution obtained was dropped into a mixed solution, which is cooledwith ice, of 3.53 g of 2,3-di-p-tolylpyrazine that is an intermediateobtained in Step 1 of Synthetic Example 4 and 25 mL of tetrahydrofuran,and stirred for 12 hours at a room temperature. This mixture was addedwith water, and an organic layer was extracted with dichloromethane. Theorganic layer obtained washed with water and dried with anhydrousmagnesium sulfate. The solution after drying was added with activatedmanganese dioxide excessively and filtration was conducted. A solvent ofthis solution was distilled off. A residue obtained by the distillationwas purified by silica gel column chromatography which usesdichloromethane as a developing solvent; thereby obtaining an objectivepyrazine derivative HMdppr-3FP (orange powder, yield of 8%). A syntheticscheme of Step 1 is shown in the following (a-6).

<Step 2: Synthesis ofdi-μ-chloro-bis{bis[5-(3-fluorophenyl)-2,3-di-p-tolylpyrazinato]iridium(III)}(abbreviation: [Ir(Mdppr-3FP)₂Cl]₂)>

Next, 12 mL of 2-ethoxyethanol, 4 mL of water, 0.14 g of the pyrazinederivative HMdppr-3FP obtained in the above Step 1, and 0.06 g ofiridium chloride hydrate (IrCl₃.H₂O) (produced by Sigma-Aldrich Corp.)were put in an eggplant-type flask with a reflux pipe, and the insideair of the flask was substituted by argon. Then, a reaction was carriedout by irradiation with microwave (2.45 GHz, 100 W) for 30 minutes. Ared powder precipitated from the reacted solution was filtered andwashed with ethanol; thereby obtaining a dinuclear complex[Ir(Mdppr-3FP)₂Cl]₂ (yield of 16%). The irradiation of microwave wasconducted using a microwave synthesis system (Discovery, manufactured byCEM Corporation). A synthetic scheme of Step 2 is shown in the following(b-6).

<Step 3: Synthesis of(acetylacetonato)bis[5-(3-fluorophenyl)2,3-di-p-tolylpyrazinato]iridium(III)(abbreviation: [Ir(Mdppr-3FP)₂(acac)]>

Next, 3 mL of 2-ethoxyethanol, 0.03 g of the dinuclear complex[Ir(Mdppr-3FP)₂Cl]₂ obtained in the above Step 2, 0.005 mL ofacetylacetone, and 0.02 g of sodium carbonate were put in aneggplant-type flask with a reflux pipe, and the inside air of the flaskwas substituted by argon. Then, a reaction was carried out byirradiation with microwave (2.45 GHz, 100 W) for 15 minutes. The reactedsolution was filtered, and then a solvent of the obtained filtrate wasdistilled off. A residue obtained by the distillation was purified bysilica gel column chromatography which uses dichloromethane as adeveloping solvent; thereby obtaining an organometallic complex of thepresent invention, [Ir(Mdppr-3FP)₂(acac)] (red powder, yield of 50%). Asynthetic scheme of Step 3 is shown in the following (c-6).

An analysis result of the red powder obtained in Step 3 by nuclearmagnetic resonance spectrometry (¹H-NMR) is shown below. A ¹H-NMR chartis shown in FIGS. 38A and 38B. From FIGS. 38A and 38B, it was found thatthe organometallic complex [Ir(Mdppr-3FP)₂(acac)] of the presentinvention represented by the above structural formula (45) was obtainedin Synthetic Example 7.

¹H-NMR. δ (CDCl₃): 1.92 (s, 6H), 2.03 (s, 6H), 2.49 (s, 6H), 5.36 (s,1H), 6.27 (s, 2H), 6.37 (dd, 2H), 6.90 (d, 2H), 7.15 (m, 2H), 7.34 (d,4H), 7.46 (m, 2H), 7.71 (d, 4H), 7.82 (m, 4H), 8.87 (s, 2H).

Next, an absorption spectrum of [Ir(Mdppr-3FP)₂(acac)] was measured withthe use of an ultraviolet-visible light spectrophotometer (manufacturedby Japan Spectroscopy Corporation, V550 type). The measurement wasconducted by using a dichloromethane solution (0.010 mmol/L) at a roomtemperature. In addition, an emission spectrum of [Ir(Mdppr-3FP)₂(acac)]was measured with the use of a fluorescence spectrophotometer(manufactured by Hamamatsu Photonics Corporation, FS920). Themeasurement was conducted by using a degassed dichloromethane solution(0.35 mmol/L) at a room temperature. FIG. 39 shows the measurementresults. The horizontal axis indicates a wavelength and the verticalaxis indicates a molar absorption coefficient and emission intensity.Note that the excitation wavelength was set at 468 nm.

As shown in FIG. 39, the organometallic complex [Ir(Mdppr-3FP)₂(acac)]of the present invention has a peak of emission spectrum at 627 nm, andred light was observed from the solution.

This application is based on Japanese Patent Application serial No.2006-077899 filed in Japan Patent Office on Mar. 21, 2006, the entirecontents of which are hereby incorporated by references.

What is claimed is:
 1. The organometallic complex is represented byformula (1):


2. The organometallic complex is represented by formula (20):